<?xml version="1.0" encoding="US-ASCII"?>
<!--XBRL Document Created with Wdesk from Workiva-->
<!-- -->
<link:linkbase xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd" xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <link:roleRef roleURI="http://corporate.comcast.com/role/CommitmentsAndContingencies" xlink:href="cmcsa-20200331.xsd#CommitmentsAndContingencies" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/CommitmentsAndContingenciesNarrativeDetails" xlink:href="cmcsa-20200331.xsd#CommitmentsAndContingenciesNarrativeDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/CondensedConsolidatedBalanceSheet" xlink:href="cmcsa-20200331.xsd#CondensedConsolidatedBalanceSheet" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/CondensedConsolidatedBalanceSheetParenthetical" xlink:href="cmcsa-20200331.xsd#CondensedConsolidatedBalanceSheetParenthetical" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/CondensedConsolidatedFinancialStatements" xlink:href="cmcsa-20200331.xsd#CondensedConsolidatedFinancialStatements" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/CondensedConsolidatedStatementOfCashFlows" xlink:href="cmcsa-20200331.xsd#CondensedConsolidatedStatementOfCashFlows" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/CondensedConsolidatedStatementOfChangesInEquity" xlink:href="cmcsa-20200331.xsd#CondensedConsolidatedStatementOfChangesInEquity" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/CondensedConsolidatedStatementOfComprehensiveIncome" xlink:href="cmcsa-20200331.xsd#CondensedConsolidatedStatementOfComprehensiveIncome" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/CondensedConsolidatedStatementOfComprehensiveIncomeParenthetical" xlink:href="cmcsa-20200331.xsd#CondensedConsolidatedStatementOfComprehensiveIncomeParenthetical" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/CondensedConsolidatedStatementOfIncome" xlink:href="cmcsa-20200331.xsd#CondensedConsolidatedStatementOfIncome" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/DocumentAndEntityInformation" xlink:href="cmcsa-20200331.xsd#DocumentAndEntityInformation" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/EarningsPerShare" xlink:href="cmcsa-20200331.xsd#EarningsPerShare" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/EarningsPerShareDetails" xlink:href="cmcsa-20200331.xsd#EarningsPerShareDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/EarningsPerShareTables" xlink:href="cmcsa-20200331.xsd#EarningsPerShareTables" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/IntangibleAssets" xlink:href="cmcsa-20200331.xsd#IntangibleAssets" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/IntangibleAssetsAmortizationOfIntangibleAssetsDetails" xlink:href="cmcsa-20200331.xsd#IntangibleAssetsAmortizationOfIntangibleAssetsDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/IntangibleAssetsSummaryOfIntangibleAssetsDetails" xlink:href="cmcsa-20200331.xsd#IntangibleAssetsSummaryOfIntangibleAssetsDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/IntangibleAssetsTables" xlink:href="cmcsa-20200331.xsd#IntangibleAssetsTables" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/Investments" xlink:href="cmcsa-20200331.xsd#Investments" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/InvestmentsEquityMethodInvestmentsDetails" xlink:href="cmcsa-20200331.xsd#InvestmentsEquityMethodInvestmentsDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/InvestmentsInvestmentAndOtherIncomeLossNetDetails" xlink:href="cmcsa-20200331.xsd#InvestmentsInvestmentAndOtherIncomeLossNetDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/InvestmentsMarketableEquitySecuritiesDetails" xlink:href="cmcsa-20200331.xsd#InvestmentsMarketableEquitySecuritiesDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/InvestmentsOtherInvestmentsDetails" xlink:href="cmcsa-20200331.xsd#InvestmentsOtherInvestmentsDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/InvestmentsScheduleOfInvestmentsDetails" xlink:href="cmcsa-20200331.xsd#InvestmentsScheduleOfInvestmentsDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/InvestmentsTables" xlink:href="cmcsa-20200331.xsd#InvestmentsTables" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/LongTermDebt" xlink:href="cmcsa-20200331.xsd#LongTermDebt" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/LongTermDebtNarrativeDetails" xlink:href="cmcsa-20200331.xsd#LongTermDebtNarrativeDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/ProgrammingAndProductionCosts" xlink:href="cmcsa-20200331.xsd#ProgrammingAndProductionCosts" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/ProgrammingAndProductionCostsCapitalizedFilmAndTelevisionCostsAndProgrammingRightsDetails" xlink:href="cmcsa-20200331.xsd#ProgrammingAndProductionCostsCapitalizedFilmAndTelevisionCostsAndProgrammingRightsDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/ProgrammingAndProductionCostsEstimatedFutureAmortizationExpenseForCapitalizedFilmAndTelevisionCostsAndProgrammingRightsDetails" xlink:href="cmcsa-20200331.xsd#ProgrammingAndProductionCostsEstimatedFutureAmortizationExpenseForCapitalizedFilmAndTelevisionCostsAndProgrammingRightsDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/ProgrammingAndProductionCostsRecognizedProgrammingAndProductionCostsDetails" xlink:href="cmcsa-20200331.xsd#ProgrammingAndProductionCostsRecognizedProgrammingAndProductionCostsDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/ProgrammingAndProductionCostsTables" xlink:href="cmcsa-20200331.xsd#ProgrammingAndProductionCostsTables" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/RecentAccountingPronouncements" xlink:href="cmcsa-20200331.xsd#RecentAccountingPronouncements" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/RecentAccountingPronouncementsNarrativeDetails" xlink:href="cmcsa-20200331.xsd#RecentAccountingPronouncementsNarrativeDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/RecentAccountingPronouncementsPolicies" xlink:href="cmcsa-20200331.xsd#RecentAccountingPronouncementsPolicies" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/Revenue" xlink:href="cmcsa-20200331.xsd#Revenue" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/RevenueCondensedConsolidatedBalanceSheetDetails" xlink:href="cmcsa-20200331.xsd#RevenueCondensedConsolidatedBalanceSheetDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/RevenueDetails" xlink:href="cmcsa-20200331.xsd#RevenueDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/RevenueRevenueByGeographicLocationDetails" xlink:href="cmcsa-20200331.xsd#RevenueRevenueByGeographicLocationDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/RevenueTables" xlink:href="cmcsa-20200331.xsd#RevenueTables" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/SegmentInformation" xlink:href="cmcsa-20200331.xsd#SegmentInformation" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/SegmentInformationDetails" xlink:href="cmcsa-20200331.xsd#SegmentInformationDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/SegmentInformationReconciliationOfAdjustedEbitdaFromSegmentToConsolidatedStatementsDetails" xlink:href="cmcsa-20200331.xsd#SegmentInformationReconciliationOfAdjustedEbitdaFromSegmentToConsolidatedStatementsDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/SegmentInformationTables" xlink:href="cmcsa-20200331.xsd#SegmentInformationTables" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/SignificantTransactions" xlink:href="cmcsa-20200331.xsd#SignificantTransactions" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/SignificantTransactionsUniversalBeijingResortDetails" xlink:href="cmcsa-20200331.xsd#SignificantTransactionsUniversalBeijingResortDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/SupplementalFinancialInformation" xlink:href="cmcsa-20200331.xsd#SupplementalFinancialInformation" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/SupplementalFinancialInformationCashCashEquivalentsAndRestrictedCashDetails" xlink:href="cmcsa-20200331.xsd#SupplementalFinancialInformationCashCashEquivalentsAndRestrictedCashDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/SupplementalFinancialInformationCashPaymentsForInterestAndIncomeTaxesDetails" xlink:href="cmcsa-20200331.xsd#SupplementalFinancialInformationCashPaymentsForInterestAndIncomeTaxesDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/SupplementalFinancialInformationComponentsOfAccumulatedOtherComprehensiveIncomeLossDetails" xlink:href="cmcsa-20200331.xsd#SupplementalFinancialInformationComponentsOfAccumulatedOtherComprehensiveIncomeLossDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/SupplementalFinancialInformationNoncashActivitiesDetails" xlink:href="cmcsa-20200331.xsd#SupplementalFinancialInformationNoncashActivitiesDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/SupplementalFinancialInformationShareBasedCompensationDetails" xlink:href="cmcsa-20200331.xsd#SupplementalFinancialInformationShareBasedCompensationDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://corporate.comcast.com/role/SupplementalFinancialInformationTables" xlink:href="cmcsa-20200331.xsd#SupplementalFinancialInformationTables" xlink:type="simple" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all" xlink:type="simple" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default" xlink:type="simple" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain" xlink:type="simple" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member" xlink:type="simple" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension" xlink:type="simple" />
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/CommitmentsAndContingencies" xlink:type="extended" />
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/CommitmentsAndContingenciesNarrativeDetails" xlink:type="extended">
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_CommitmentAndContingenciesLineItems" xlink:label="loc_cmcsa_CommitmentAndContingenciesLineItems_9B8F4514254D25431F1AAD5094CD641B" xlink:type="locator" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_CommitmentAndContingenciesTable" xlink:label="loc_cmcsa_CommitmentAndContingenciesTable_277283DE41975E6DE3EEAD5094C9D0EF" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_cmcsa_CommitmentAndContingenciesLineItems_9B8F4514254D25431F1AAD5094CD641B" xlink:to="loc_cmcsa_CommitmentAndContingenciesTable_277283DE41975E6DE3EEAD5094C9D0EF" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_A20402830D431ACA86C0AD5094CA5A8F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_cmcsa_CommitmentAndContingenciesTable_277283DE41975E6DE3EEAD5094C9D0EF" xlink:to="loc_dei_LegalEntityAxis_A20402830D431ACA86C0AD5094CA5A8F" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_0EA5685C25DCAA0C79B3AD5094CB1994_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_A20402830D431ACA86C0AD5094CA5A8F" xlink:to="loc_dei_EntityDomain_0EA5685C25DCAA0C79B3AD5094CB1994_default" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_0EA5685C25DCAA0C79B3AD5094CB1994" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_A20402830D431ACA86C0AD5094CA5A8F" xlink:to="loc_dei_EntityDomain_0EA5685C25DCAA0C79B3AD5094CB1994" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_NbcuniversalEnterpriseMember" xlink:label="loc_cmcsa_NbcuniversalEnterpriseMember_DE63287734DE722653B2AD5094CBAC62" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_0EA5685C25DCAA0C79B3AD5094CB1994" xlink:to="loc_cmcsa_NbcuniversalEnterpriseMember_DE63287734DE722653B2AD5094CBAC62" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementClassOfStockAxis" xlink:label="loc_us-gaap_StatementClassOfStockAxis_F2C5F5A693D0E64B060CAD5094CC27B4" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_cmcsa_CommitmentAndContingenciesTable_277283DE41975E6DE3EEAD5094C9D0EF" xlink:to="loc_us-gaap_StatementClassOfStockAxis_F2C5F5A693D0E64B060CAD5094CC27B4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ClassOfStockDomain" xlink:label="loc_us-gaap_ClassOfStockDomain_269A37E8040D7B2507A3AD5094CC0519_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_F2C5F5A693D0E64B060CAD5094CC27B4" xlink:to="loc_us-gaap_ClassOfStockDomain_269A37E8040D7B2507A3AD5094CC0519_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ClassOfStockDomain" xlink:label="loc_us-gaap_ClassOfStockDomain_269A37E8040D7B2507A3AD5094CC0519" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_F2C5F5A693D0E64B060CAD5094CC27B4" xlink:to="loc_us-gaap_ClassOfStockDomain_269A37E8040D7B2507A3AD5094CC0519" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_RedeemablePreferredStockMember" xlink:label="loc_us-gaap_RedeemablePreferredStockMember_23B71A2A9BCE07EC95D4AD5094CCE48E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_269A37E8040D7B2507A3AD5094CC0519" xlink:to="loc_us-gaap_RedeemablePreferredStockMember_23B71A2A9BCE07EC95D4AD5094CCE48E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_16C84E68203D598BD63EAD5094CC1DBE" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_cmcsa_CommitmentAndContingenciesTable_277283DE41975E6DE3EEAD5094C9D0EF" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_16C84E68203D598BD63EAD5094CC1DBE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_8AE753207DB9F9E471DDAD5094CD9B7E_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_16C84E68203D598BD63EAD5094CC1DBE" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_8AE753207DB9F9E471DDAD5094CD9B7E_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_8AE753207DB9F9E471DDAD5094CD9B7E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_16C84E68203D598BD63EAD5094CC1DBE" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_8AE753207DB9F9E471DDAD5094CD9B7E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueInputsLevel2Member" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_E82E64FFCFBD370351F3AD5094CD7E66" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_8AE753207DB9F9E471DDAD5094CD9B7E" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_E82E64FFCFBD370351F3AD5094CD7E66" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_PreferredStockPutPeriod" xlink:label="loc_cmcsa_PreferredStockPutPeriod_F3D41BA29E6B1E785837AD5094CDF5C9" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_CommitmentAndContingenciesLineItems_9B8F4514254D25431F1AAD5094CD641B" xlink:to="loc_cmcsa_PreferredStockPutPeriod_F3D41BA29E6B1E785837AD5094CDF5C9" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_TemporaryEquityFairValueOfRedeemableSubsidiaryPreferredStock" xlink:label="loc_cmcsa_TemporaryEquityFairValueOfRedeemableSubsidiaryPreferredStock_DD32FB80662219910778AD5094CE42D1" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_CommitmentAndContingenciesLineItems_9B8F4514254D25431F1AAD5094CD641B" xlink:to="loc_cmcsa_TemporaryEquityFairValueOfRedeemableSubsidiaryPreferredStock_DD32FB80662219910778AD5094CE42D1" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/CondensedConsolidatedBalanceSheet" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_61855129113FDA951532C3560A23DC9E" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_2D2C4F0C85E69731E995C3560A2219A0" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_61855129113FDA951532C3560A23DC9E" xlink:to="loc_us-gaap_StatementTable_2D2C4F0C85E69731E995C3560A2219A0" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementClassOfStockAxis" xlink:label="loc_us-gaap_StatementClassOfStockAxis_1195B846CE5701565B2CC3560A22B122" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_2D2C4F0C85E69731E995C3560A2219A0" xlink:to="loc_us-gaap_StatementClassOfStockAxis_1195B846CE5701565B2CC3560A22B122" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ClassOfStockDomain" xlink:label="loc_us-gaap_ClassOfStockDomain_FDB0222F849651C213A9C3560A225D6D_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_1195B846CE5701565B2CC3560A22B122" xlink:to="loc_us-gaap_ClassOfStockDomain_FDB0222F849651C213A9C3560A225D6D_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ClassOfStockDomain" xlink:label="loc_us-gaap_ClassOfStockDomain_FDB0222F849651C213A9C3560A225D6D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_1195B846CE5701565B2CC3560A22B122" xlink:to="loc_us-gaap_ClassOfStockDomain_FDB0222F849651C213A9C3560A225D6D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CommonClassAMember" xlink:label="loc_us-gaap_CommonClassAMember_3CB404CBEC0997BCB83AC3560A239F1A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_FDB0222F849651C213A9C3560A225D6D" xlink:to="loc_us-gaap_CommonClassAMember_3CB404CBEC0997BCB83AC3560A239F1A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CommonClassBMember" xlink:label="loc_us-gaap_CommonClassBMember_86907D4B0BA2F12F11DAC3560A231765" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_FDB0222F849651C213A9C3560A225D6D" xlink:to="loc_us-gaap_CommonClassBMember_86907D4B0BA2F12F11DAC3560A231765" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AssetsAbstract" xlink:label="loc_us-gaap_AssetsAbstract_4F5B221394B386A35371C3560A2331EC" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_61855129113FDA951532C3560A23DC9E" xlink:to="loc_us-gaap_AssetsAbstract_4F5B221394B386A35371C3560A2331EC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AssetsCurrentAbstract" xlink:label="loc_us-gaap_AssetsCurrentAbstract_78FCB4EBBE44463A9643C3560A24865E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_4F5B221394B386A35371C3560A2331EC" xlink:to="loc_us-gaap_AssetsCurrentAbstract_78FCB4EBBE44463A9643C3560A24865E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_9367BCD9171CEE1E6D04C3560A247A0D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_78FCB4EBBE44463A9643C3560A24865E" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_9367BCD9171CEE1E6D04C3560A247A0D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AccountsReceivableNetCurrent" xlink:label="loc_us-gaap_AccountsReceivableNetCurrent_0EFB6E32591A3ED8DCD5C3560A25EE80" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_78FCB4EBBE44463A9643C3560A24865E" xlink:to="loc_us-gaap_AccountsReceivableNetCurrent_0EFB6E32591A3ED8DCD5C3560A25EE80" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_EntertainmentLicenseAgreementForProgramMaterialIncludingSportsRightsAdvancesCapitalizedCostCurrent" xlink:label="loc_cmcsa_EntertainmentLicenseAgreementForProgramMaterialIncludingSportsRightsAdvancesCapitalizedCostCurrent_309C2D30CF2EF3C239E0C3560A250032" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_78FCB4EBBE44463A9643C3560A24865E" xlink:to="loc_cmcsa_EntertainmentLicenseAgreementForProgramMaterialIncludingSportsRightsAdvancesCapitalizedCostCurrent_309C2D30CF2EF3C239E0C3560A250032" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_ProgrammingRightsCurrent" xlink:label="loc_cmcsa_ProgrammingRightsCurrent_F59E9B5445CB687D5772C3560A2557D2" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_78FCB4EBBE44463A9643C3560A24865E" xlink:to="loc_cmcsa_ProgrammingRightsCurrent_F59E9B5445CB687D5772C3560A2557D2" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OtherAssetsCurrent" xlink:label="loc_us-gaap_OtherAssetsCurrent_9688C31965B4DABE0C09C3560A252DB5" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_78FCB4EBBE44463A9643C3560A24865E" xlink:to="loc_us-gaap_OtherAssetsCurrent_9688C31965B4DABE0C09C3560A252DB5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AssetsCurrent" xlink:label="loc_us-gaap_AssetsCurrent_3566EBC6F51F69BB3077C3560A25D673" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_78FCB4EBBE44463A9643C3560A24865E" xlink:to="loc_us-gaap_AssetsCurrent_3566EBC6F51F69BB3077C3560A25D673" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_FilmMonetizedOnItsOwnAndEntertainmentLicenseAgreementForProgramMaterialIncludingSportsRightsAdvancesCapitalizedCostsNoncurrent" xlink:label="loc_cmcsa_FilmMonetizedOnItsOwnAndEntertainmentLicenseAgreementForProgramMaterialIncludingSportsRightsAdvancesCapitalizedCostsNoncurrent_4210B0B29705CC3410EEC3560A263C21" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_4F5B221394B386A35371C3560A2331EC" xlink:to="loc_cmcsa_FilmMonetizedOnItsOwnAndEntertainmentLicenseAgreementForProgramMaterialIncludingSportsRightsAdvancesCapitalizedCostsNoncurrent_4210B0B29705CC3410EEC3560A263C21" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_FilmAndTelevisionCosts" xlink:label="loc_cmcsa_FilmAndTelevisionCosts_D285CA232A15254CCBD4C3560A260771" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_4F5B221394B386A35371C3560A2331EC" xlink:to="loc_cmcsa_FilmAndTelevisionCosts_D285CA232A15254CCBD4C3560A260771" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LongTermInvestments" xlink:label="loc_us-gaap_LongTermInvestments_BEB428264DC411557FF8C3560A26F9A4" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_4F5B221394B386A35371C3560A2331EC" xlink:to="loc_us-gaap_LongTermInvestments_BEB428264DC411557FF8C3560A26F9A4" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_InvestmentSecuringCollateralizedObligation" xlink:label="loc_cmcsa_InvestmentSecuringCollateralizedObligation_211DDE7F17ADED4E3B06C3560A26EF6B" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_4F5B221394B386A35371C3560A2331EC" xlink:to="loc_cmcsa_InvestmentSecuringCollateralizedObligation_211DDE7F17ADED4E3B06C3560A26EF6B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PropertyPlantAndEquipmentNet" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_FF0AEA2010C140C3AEFDC3560A2621E5" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_4F5B221394B386A35371C3560A2331EC" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_FF0AEA2010C140C3AEFDC3560A2621E5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_Goodwill" xlink:label="loc_us-gaap_Goodwill_3B2E979D133C5E9D5790C3560A265A94" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_4F5B221394B386A35371C3560A2331EC" xlink:to="loc_us-gaap_Goodwill_3B2E979D133C5E9D5790C3560A265A94" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_IndefiniteLivedFranchiseRights" xlink:label="loc_us-gaap_IndefiniteLivedFranchiseRights_D3069518164120502B26C3560A27D098" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_4F5B221394B386A35371C3560A2331EC" xlink:to="loc_us-gaap_IndefiniteLivedFranchiseRights_D3069518164120502B26C3560A27D098" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OtherIntangibleAssetsNet" xlink:label="loc_us-gaap_OtherIntangibleAssetsNet_E951CE2A02896033F1CDC3560A273EFB" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_4F5B221394B386A35371C3560A2331EC" xlink:to="loc_us-gaap_OtherIntangibleAssetsNet_E951CE2A02896033F1CDC3560A273EFB" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OtherAssetsNoncurrent" xlink:label="loc_us-gaap_OtherAssetsNoncurrent_0AAF64E6151339F609C6C3560A2763B1" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_4F5B221394B386A35371C3560A2331EC" xlink:to="loc_us-gaap_OtherAssetsNoncurrent_0AAF64E6151339F609C6C3560A2763B1" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_Assets" xlink:label="loc_us-gaap_Assets_91038492AF92266305B9C3560A2712C2" xlink:type="locator" />
    <link:definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_4F5B221394B386A35371C3560A2331EC" xlink:to="loc_us-gaap_Assets_91038492AF92266305B9C3560A2712C2" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LiabilitiesAndStockholdersEquityAbstract" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_28520118139C3C828527C3560A27D22B" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_61855129113FDA951532C3560A23DC9E" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_28520118139C3C828527C3560A27D22B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LiabilitiesCurrentAbstract" xlink:label="loc_us-gaap_LiabilitiesCurrentAbstract_2DADA0AB1247456D1DA3C3560A2702C1" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_28520118139C3C828527C3560A27D22B" xlink:to="loc_us-gaap_LiabilitiesCurrentAbstract_2DADA0AB1247456D1DA3C3560A2702C1" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AccountsPayableCurrent" xlink:label="loc_us-gaap_AccountsPayableCurrent_1CD9B6A2D07204528F16C3560A281929" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_2DADA0AB1247456D1DA3C3560A2702C1" xlink:to="loc_us-gaap_AccountsPayableCurrent_1CD9B6A2D07204528F16C3560A281929" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_AccruedParticipationsAndResidualsCurrent" xlink:label="loc_cmcsa_AccruedParticipationsAndResidualsCurrent_CDE274C37E20049B1432C3560A28B9FA" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_2DADA0AB1247456D1DA3C3560A2702C1" xlink:to="loc_cmcsa_AccruedParticipationsAndResidualsCurrent_CDE274C37E20049B1432C3560A28B9FA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DeferredRevenueCurrent" xlink:label="loc_us-gaap_DeferredRevenueCurrent_C59AFE22448E4AA5BCADC3560A28C90B" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_2DADA0AB1247456D1DA3C3560A2702C1" xlink:to="loc_us-gaap_DeferredRevenueCurrent_C59AFE22448E4AA5BCADC3560A28C90B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AccruedLiabilitiesCurrent" xlink:label="loc_us-gaap_AccruedLiabilitiesCurrent_6F0C2360AB614B4D353EC3560A28A950" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_2DADA0AB1247456D1DA3C3560A2702C1" xlink:to="loc_us-gaap_AccruedLiabilitiesCurrent_6F0C2360AB614B4D353EC3560A28A950" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DebtCurrent" xlink:label="loc_us-gaap_DebtCurrent_5B01C4E12A0AE8DAECF1C3560A28BC7A" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_2DADA0AB1247456D1DA3C3560A2702C1" xlink:to="loc_us-gaap_DebtCurrent_5B01C4E12A0AE8DAECF1C3560A28BC7A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LiabilitiesCurrent" xlink:label="loc_us-gaap_LiabilitiesCurrent_3D967863B735DCF4D8ECC3560A293607" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_2DADA0AB1247456D1DA3C3560A2702C1" xlink:to="loc_us-gaap_LiabilitiesCurrent_3D967863B735DCF4D8ECC3560A293607" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LongTermDebtAndCapitalLeaseObligations" xlink:label="loc_us-gaap_LongTermDebtAndCapitalLeaseObligations_AF4510D090CD4057C57DC3560A2929DB" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_28520118139C3C828527C3560A27D22B" xlink:to="loc_us-gaap_LongTermDebtAndCapitalLeaseObligations_AF4510D090CD4057C57DC3560A2929DB" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_CollateralizedObligation" xlink:label="loc_cmcsa_CollateralizedObligation_C75C0853339AA36C9DA8C3560A2994F0" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_28520118139C3C828527C3560A27D22B" xlink:to="loc_cmcsa_CollateralizedObligation_C75C0853339AA36C9DA8C3560A2994F0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DeferredIncomeTaxLiabilitiesNet" xlink:label="loc_us-gaap_DeferredIncomeTaxLiabilitiesNet_70AE34FDDA91037D670CC3560A29009B" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_28520118139C3C828527C3560A27D22B" xlink:to="loc_us-gaap_DeferredIncomeTaxLiabilitiesNet_70AE34FDDA91037D670CC3560A29009B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OtherLiabilitiesNoncurrent" xlink:label="loc_us-gaap_OtherLiabilitiesNoncurrent_210E274C0A166CAAF8FDC3560A297C13" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_28520118139C3C828527C3560A27D22B" xlink:to="loc_us-gaap_OtherLiabilitiesNoncurrent_210E274C0A166CAAF8FDC3560A297C13" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CommitmentsAndContingencies" xlink:label="loc_us-gaap_CommitmentsAndContingencies_781BAD138C5A4E792E20C3560A2A221A" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_28520118139C3C828527C3560A27D22B" xlink:to="loc_us-gaap_CommitmentsAndContingencies_781BAD138C5A4E792E20C3560A2A221A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_RedeemableNoncontrollingInterestEquityCarryingAmount" xlink:label="loc_us-gaap_RedeemableNoncontrollingInterestEquityCarryingAmount_02232B04E48165AB9A7FC3560A2ABDD3" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_28520118139C3C828527C3560A27D22B" xlink:to="loc_us-gaap_RedeemableNoncontrollingInterestEquityCarryingAmount_02232B04E48165AB9A7FC3560A2ABDD3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_B8E6338967F44732930DC3560A2AD23B" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_28520118139C3C828527C3560A27D22B" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_B8E6338967F44732930DC3560A2AD23B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PreferredStockValue" xlink:label="loc_us-gaap_PreferredStockValue_8DB3749CE23D7275776EC3560A2A00EE" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_B8E6338967F44732930DC3560A2AD23B" xlink:to="loc_us-gaap_PreferredStockValue_8DB3749CE23D7275776EC3560A2A00EE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CommonStockValue" xlink:label="loc_us-gaap_CommonStockValue_4958E5D0C7621D139C61C3560A2A1F8E" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_B8E6338967F44732930DC3560A2AD23B" xlink:to="loc_us-gaap_CommonStockValue_4958E5D0C7621D139C61C3560A2A1F8E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AdditionalPaidInCapital" xlink:label="loc_us-gaap_AdditionalPaidInCapital_71772B82B09014E822DBC3560A2A4921" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_B8E6338967F44732930DC3560A2AD23B" xlink:to="loc_us-gaap_AdditionalPaidInCapital_71772B82B09014E822DBC3560A2A4921" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_RetainedEarningsAccumulatedDeficit" xlink:label="loc_us-gaap_RetainedEarningsAccumulatedDeficit_67C14BAAE132F4582F89C3560A2B82BC" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_B8E6338967F44732930DC3560A2AD23B" xlink:to="loc_us-gaap_RetainedEarningsAccumulatedDeficit_67C14BAAE132F4582F89C3560A2B82BC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TreasuryStockValue" xlink:label="loc_us-gaap_TreasuryStockValue_FCE6A9D64B1BD701CCA4C3560A2B1CE7" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_B8E6338967F44732930DC3560A2AD23B" xlink:to="loc_us-gaap_TreasuryStockValue_FCE6A9D64B1BD701CCA4C3560A2B1CE7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_C103ED4B430F060D714DC3560A2BC129" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_B8E6338967F44732930DC3560A2AD23B" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_C103ED4B430F060D714DC3560A2BC129" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StockholdersEquity" xlink:label="loc_us-gaap_StockholdersEquity_B3F6BAA9EBC6605D3776C3560A2B6162" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_B8E6338967F44732930DC3560A2AD23B" xlink:to="loc_us-gaap_StockholdersEquity_B3F6BAA9EBC6605D3776C3560A2B6162" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_MinorityInterest" xlink:label="loc_us-gaap_MinorityInterest_F1409AB847834C1BCB08C3560A2BA237" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_B8E6338967F44732930DC3560A2AD23B" xlink:to="loc_us-gaap_MinorityInterest_F1409AB847834C1BCB08C3560A2BA237" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_0F76680E386D90C143E2C3560A2C0EF4" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_B8E6338967F44732930DC3560A2AD23B" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_0F76680E386D90C143E2C3560A2C0EF4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LiabilitiesAndStockholdersEquity" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquity_CA40E8C2F81C967077ACC3560A2C2A06" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_28520118139C3C828527C3560A27D22B" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquity_CA40E8C2F81C967077ACC3560A2C2A06" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/CondensedConsolidatedBalanceSheetParenthetical" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_C05E7F95D9953E73FB4CAD509725C729" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_9619665B89C90B932D69AD5097238642" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_C05E7F95D9953E73FB4CAD509725C729" xlink:to="loc_us-gaap_StatementTable_9619665B89C90B932D69AD5097238642" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementClassOfStockAxis" xlink:label="loc_us-gaap_StatementClassOfStockAxis_6EFC3E801BB2777BE737AD509724DA43" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_9619665B89C90B932D69AD5097238642" xlink:to="loc_us-gaap_StatementClassOfStockAxis_6EFC3E801BB2777BE737AD509724DA43" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ClassOfStockDomain" xlink:label="loc_us-gaap_ClassOfStockDomain_5CF0EDE24A436D5EF071AD509724DF45_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_6EFC3E801BB2777BE737AD509724DA43" xlink:to="loc_us-gaap_ClassOfStockDomain_5CF0EDE24A436D5EF071AD509724DF45_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ClassOfStockDomain" xlink:label="loc_us-gaap_ClassOfStockDomain_5CF0EDE24A436D5EF071AD509724DF45" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_6EFC3E801BB2777BE737AD509724DA43" xlink:to="loc_us-gaap_ClassOfStockDomain_5CF0EDE24A436D5EF071AD509724DF45" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CommonClassAMember" xlink:label="loc_us-gaap_CommonClassAMember_C92BAD90CE3445AE993DAD50972486B0" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_5CF0EDE24A436D5EF071AD509724DF45" xlink:to="loc_us-gaap_CommonClassAMember_C92BAD90CE3445AE993DAD50972486B0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CommonClassBMember" xlink:label="loc_us-gaap_CommonClassBMember_1A56EFB602908FCE210AAD50972434A8" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_5CF0EDE24A436D5EF071AD509724DF45" xlink:to="loc_us-gaap_CommonClassBMember_1A56EFB602908FCE210AAD50972434A8" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_A9776248A0A1C289723EAD5097259C6D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_C05E7F95D9953E73FB4CAD509725C729" xlink:to="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_A9776248A0A1C289723EAD5097259C6D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_1B8E541E5BCFED452A4AAD509725B7F3" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_C05E7F95D9953E73FB4CAD509725C729" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_1B8E541E5BCFED452A4AAD509725B7F3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PreferredStockSharesAuthorized" xlink:label="loc_us-gaap_PreferredStockSharesAuthorized_2B6CAD5130C24A311A52AD5097251230" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_C05E7F95D9953E73FB4CAD509725C729" xlink:to="loc_us-gaap_PreferredStockSharesAuthorized_2B6CAD5130C24A311A52AD5097251230" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PreferredStockSharesIssued" xlink:label="loc_us-gaap_PreferredStockSharesIssued_C7D1C96CE8DD3E56E4E0AD509725891A" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_C05E7F95D9953E73FB4CAD509725C729" xlink:to="loc_us-gaap_PreferredStockSharesIssued_C7D1C96CE8DD3E56E4E0AD509725891A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CommonStockParOrStatedValuePerShare" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_2D74366E6597613C7045AD5097263BC9" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_C05E7F95D9953E73FB4CAD509725C729" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_2D74366E6597613C7045AD5097263BC9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CommonStockSharesAuthorized" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_1C7BDED102D3C6577F7FAD509726DDFB" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_C05E7F95D9953E73FB4CAD509725C729" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_1C7BDED102D3C6577F7FAD509726DDFB" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CommonStockSharesIssued" xlink:label="loc_us-gaap_CommonStockSharesIssued_342EAACF2865A399D55AAD5097260070" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_C05E7F95D9953E73FB4CAD509725C729" xlink:to="loc_us-gaap_CommonStockSharesIssued_342EAACF2865A399D55AAD5097260070" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CommonStockSharesOutstanding" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_D3C0605C9A874AF4BDC3AD509726D1EA" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_C05E7F95D9953E73FB4CAD509725C729" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_D3C0605C9A874AF4BDC3AD509726D1EA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TreasuryStockShares" xlink:label="loc_us-gaap_TreasuryStockShares_201E3C88D7BF56651BB6AD509726CBCF" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_C05E7F95D9953E73FB4CAD509725C729" xlink:to="loc_us-gaap_TreasuryStockShares_201E3C88D7BF56651BB6AD509726CBCF" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/CondensedConsolidatedFinancialStatements" xlink:type="extended" />
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/CondensedConsolidatedStatementOfCashFlows" xlink:type="extended" />
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/CondensedConsolidatedStatementOfChangesInEquity" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_9B77C42BC72AA2E50110AD509709BAA1" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_D4C79F18BF44EEE196EFAD5096FE6A6F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_9B77C42BC72AA2E50110AD509709BAA1" xlink:to="loc_us-gaap_StatementTable_D4C79F18BF44EEE196EFAD5096FE6A6F" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementClassOfStockAxis" xlink:label="loc_us-gaap_StatementClassOfStockAxis_D836A01BAA5094512AF1AD5096FEEEBE" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_D4C79F18BF44EEE196EFAD5096FE6A6F" xlink:to="loc_us-gaap_StatementClassOfStockAxis_D836A01BAA5094512AF1AD5096FEEEBE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ClassOfStockDomain" xlink:label="loc_us-gaap_ClassOfStockDomain_D427E5C3C2B057AFFD2BAD5096FE1AC9_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_D836A01BAA5094512AF1AD5096FEEEBE" xlink:to="loc_us-gaap_ClassOfStockDomain_D427E5C3C2B057AFFD2BAD5096FE1AC9_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ClassOfStockDomain" xlink:label="loc_us-gaap_ClassOfStockDomain_D427E5C3C2B057AFFD2BAD5096FE1AC9" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_D836A01BAA5094512AF1AD5096FEEEBE" xlink:to="loc_us-gaap_ClassOfStockDomain_D427E5C3C2B057AFFD2BAD5096FE1AC9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CommonClassAMember" xlink:label="loc_us-gaap_CommonClassAMember_367FD73E5F22520AC536AD5096FF6F0C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_D427E5C3C2B057AFFD2BAD5096FE1AC9" xlink:to="loc_us-gaap_CommonClassAMember_367FD73E5F22520AC536AD5096FF6F0C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_18E43CD822CDFD240EB9AD5096FF8877" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_D4C79F18BF44EEE196EFAD5096FE6A6F" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_18E43CD822CDFD240EB9AD5096FF8877" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaap_EquityComponentDomain_B70041C1E95612C56D70AD5096FF1323_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_18E43CD822CDFD240EB9AD5096FF8877" xlink:to="loc_us-gaap_EquityComponentDomain_B70041C1E95612C56D70AD5096FF1323_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaap_EquityComponentDomain_B70041C1E95612C56D70AD5096FF1323" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_18E43CD822CDFD240EB9AD5096FF8877" xlink:to="loc_us-gaap_EquityComponentDomain_B70041C1E95612C56D70AD5096FF1323" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_RedeemableNoncontrollingInterestsAndRedeemableSubsidiaryPreferredStockMember" xlink:label="loc_cmcsa_RedeemableNoncontrollingInterestsAndRedeemableSubsidiaryPreferredStockMember_AD36BB226F1113216B7FAD509704B7B5" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_B70041C1E95612C56D70AD5096FF1323" xlink:to="loc_cmcsa_RedeemableNoncontrollingInterestsAndRedeemableSubsidiaryPreferredStockMember_AD36BB226F1113216B7FAD509704B7B5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CommonStockMember" xlink:label="loc_us-gaap_CommonStockMember_446929CBCDB542EFD383AD509707586B" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_B70041C1E95612C56D70AD5096FF1323" xlink:to="loc_us-gaap_CommonStockMember_446929CBCDB542EFD383AD509707586B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AdditionalPaidInCapitalMember" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_09C22C0DD31335B785C8AD509707DBF1" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_B70041C1E95612C56D70AD5096FF1323" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_09C22C0DD31335B785C8AD509707DBF1" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_RetainedEarningsMember" xlink:label="loc_us-gaap_RetainedEarningsMember_5ACE92B1A6EBA6A7E4AFAD50970859CC" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_B70041C1E95612C56D70AD5096FF1323" xlink:to="loc_us-gaap_RetainedEarningsMember_5ACE92B1A6EBA6A7E4AFAD50970859CC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TreasuryStockMember" xlink:label="loc_us-gaap_TreasuryStockMember_EBEEB72018F3D37E85AFAD50970841E9" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_B70041C1E95612C56D70AD5096FF1323" xlink:to="loc_us-gaap_TreasuryStockMember_EBEEB72018F3D37E85AFAD50970841E9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_1C55B43342A5C0562366AD5097086E4D" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_B70041C1E95612C56D70AD5096FF1323" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_1C55B43342A5C0562366AD5097086E4D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_NoncontrollingInterestMember" xlink:label="loc_us-gaap_NoncontrollingInterestMember_8304622142CF979EB06DAD5097086786" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_B70041C1E95612C56D70AD5096FF1323" xlink:to="loc_us-gaap_NoncontrollingInterestMember_8304622142CF979EB06DAD5097086786" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_IncreaseDecreaseInTemporaryEquityRollForward" xlink:label="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_4FE0076FAE8465BD535DAD50970CB053" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_9B77C42BC72AA2E50110AD509709BAA1" xlink:to="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_4FE0076FAE8465BD535DAD50970CB053" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_RedeemableNoncontrollingInterestEquityCarryingAmount" xlink:label="loc_us-gaap_RedeemableNoncontrollingInterestEquityCarryingAmount_D4FDB5A408845C67B22FAD50970D92D3" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_4FE0076FAE8465BD535DAD50970CB053" xlink:to="loc_us-gaap_RedeemableNoncontrollingInterestEquityCarryingAmount_D4FDB5A408845C67B22FAD50970D92D3" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_ContributionsFromAndDistributionsToNoncontrollingInterestsAttributableToTemporaryEquity" xlink:label="loc_cmcsa_ContributionsFromAndDistributionsToNoncontrollingInterestsAttributableToTemporaryEquity_A035C4049856C794BFFDAD50970D6059" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_4FE0076FAE8465BD535DAD50970CB053" xlink:to="loc_cmcsa_ContributionsFromAndDistributionsToNoncontrollingInterestsAttributableToTemporaryEquity_A035C4049856C794BFFDAD50970D6059" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TemporaryEquityOtherChanges" xlink:label="loc_us-gaap_TemporaryEquityOtherChanges_A37AF12BF32505DF79F3AD50970E495D" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_4FE0076FAE8465BD535DAD50970CB053" xlink:to="loc_us-gaap_TemporaryEquityOtherChanges_A37AF12BF32505DF79F3AD50970E495D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_NetIncomeLossAttributableToRedeemableNoncontrollingInterest" xlink:label="loc_us-gaap_NetIncomeLossAttributableToRedeemableNoncontrollingInterest_3179F7BE71571B36ABA2AD50970E7CB3" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_4FE0076FAE8465BD535DAD50970CB053" xlink:to="loc_us-gaap_NetIncomeLossAttributableToRedeemableNoncontrollingInterest_3179F7BE71571B36ABA2AD50970E7CB3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_4735D34609BA7D50621EAD509710457E" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_9B77C42BC72AA2E50110AD509709BAA1" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_4735D34609BA7D50621EAD509710457E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_3A673705645D717F83C2AD50971205D5" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_4735D34609BA7D50621EAD509710457E" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_3A673705645D717F83C2AD50971205D5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption" xlink:label="loc_us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption_C2AACB9C1ABE3F3D9E0CAD509714003D" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_4735D34609BA7D50621EAD509710457E" xlink:to="loc_us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption_C2AACB9C1ABE3F3D9E0CAD509714003D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_9CE3E9495EDA1D4E1729AD509714E929" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_4735D34609BA7D50621EAD509710457E" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_9CE3E9495EDA1D4E1729AD509714E929" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StockRepurchasedAndRetiredDuringPeriodValue" xlink:label="loc_us-gaap_StockRepurchasedAndRetiredDuringPeriodValue_A4E43577E9E345219CE2AD509715E963" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_4735D34609BA7D50621EAD509710457E" xlink:to="loc_us-gaap_StockRepurchasedAndRetiredDuringPeriodValue_A4E43577E9E345219CE2AD509715E963" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan_AC8A99743C815B9594CAAD509715E493" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_4735D34609BA7D50621EAD509710457E" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan_AC8A99743C815B9594CAAD509715E493" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DividendsCommonStockCash" xlink:label="loc_us-gaap_DividendsCommonStockCash_04491F5BAA920FDC59BCAD509715EC76" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_4735D34609BA7D50621EAD509710457E" xlink:to="loc_us-gaap_DividendsCommonStockCash_04491F5BAA920FDC59BCAD509715EC76" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTax" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_B8125D649EF7A3E4A50EAD509715E749" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_4735D34609BA7D50621EAD509710457E" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_B8125D649EF7A3E4A50EAD509715E749" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_ContributionsFromAndDistributionsToNoncontrollingInterests" xlink:label="loc_cmcsa_ContributionsFromAndDistributionsToNoncontrollingInterests_6CDE99E715B268B24AFFAD5097160CAC" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_4735D34609BA7D50621EAD509710457E" xlink:to="loc_cmcsa_ContributionsFromAndDistributionsToNoncontrollingInterests_6CDE99E715B268B24AFFAD5097160CAC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StockholdersEquityOther" xlink:label="loc_us-gaap_StockholdersEquityOther_221213D3EE748A273D0EAD509716C865" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_4735D34609BA7D50621EAD509710457E" xlink:to="loc_us-gaap_StockholdersEquityOther_221213D3EE748A273D0EAD509716C865" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_NetIncomeLoss" xlink:label="loc_us-gaap_NetIncomeLoss_AE728E6F0108BA69F3C8AD509716465D" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_4735D34609BA7D50621EAD509710457E" xlink:to="loc_us-gaap_NetIncomeLoss_AE728E6F0108BA69F3C8AD509716465D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_NetIncomeLossAttributableToNoncontrollingInterest" xlink:label="loc_us-gaap_NetIncomeLossAttributableToNoncontrollingInterest_129BDF770BFAB7610EFAAD50971716DF" xlink:type="locator" />
    <link:definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_4735D34609BA7D50621EAD509710457E" xlink:to="loc_us-gaap_NetIncomeLossAttributableToNoncontrollingInterest_129BDF770BFAB7610EFAAD50971716DF" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CommonStockDividendsPerShareDeclared" xlink:label="loc_us-gaap_CommonStockDividendsPerShareDeclared_98646500CAEF04A82651AD509717D440" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_9B77C42BC72AA2E50110AD509709BAA1" xlink:to="loc_us-gaap_CommonStockDividendsPerShareDeclared_98646500CAEF04A82651AD509717D440" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/CondensedConsolidatedStatementOfComprehensiveIncome" xlink:type="extended" />
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/CondensedConsolidatedStatementOfComprehensiveIncomeParenthetical" xlink:type="extended" />
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/CondensedConsolidatedStatementOfIncome" xlink:type="extended" />
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/DocumentAndEntityInformation" xlink:type="extended">
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_DocumentAndEntityInformationLineItems" xlink:label="loc_cmcsa_DocumentAndEntityInformationLineItems_1F0DF4A2D541D54EFC01C659D7A9A975" xlink:type="locator" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_DocumentAndEntityInformationTable" xlink:label="loc_cmcsa_DocumentAndEntityInformationTable_975ABEE11FA2C9564A3EC659D7A5B8CD" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_cmcsa_DocumentAndEntityInformationLineItems_1F0DF4A2D541D54EFC01C659D7A9A975" xlink:to="loc_cmcsa_DocumentAndEntityInformationTable_975ABEE11FA2C9564A3EC659D7A5B8CD" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementClassOfStockAxis" xlink:label="loc_us-gaap_StatementClassOfStockAxis_6FB97D4A431328DFD22EC659D7A64CB1" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_cmcsa_DocumentAndEntityInformationTable_975ABEE11FA2C9564A3EC659D7A5B8CD" xlink:to="loc_us-gaap_StatementClassOfStockAxis_6FB97D4A431328DFD22EC659D7A64CB1" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ClassOfStockDomain" xlink:label="loc_us-gaap_ClassOfStockDomain_7DE9A07153E2D9BF071BC659D7A66B80_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_6FB97D4A431328DFD22EC659D7A64CB1" xlink:to="loc_us-gaap_ClassOfStockDomain_7DE9A07153E2D9BF071BC659D7A66B80_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ClassOfStockDomain" xlink:label="loc_us-gaap_ClassOfStockDomain_7DE9A07153E2D9BF071BC659D7A66B80" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_6FB97D4A431328DFD22EC659D7A64CB1" xlink:to="loc_us-gaap_ClassOfStockDomain_7DE9A07153E2D9BF071BC659D7A66B80" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CommonClassAMember" xlink:label="loc_us-gaap_CommonClassAMember_A565E37764A239271A80C659D7A62C7B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_7DE9A07153E2D9BF071BC659D7A66B80" xlink:to="loc_us-gaap_CommonClassAMember_A565E37764A239271A80C659D7A62C7B" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_Notes0.250percentDue2027Member" xlink:label="loc_cmcsa_Notes0.250percentDue2027Member_3FEEC6B8183A8FC4D0BBC659D7A726BA" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_7DE9A07153E2D9BF071BC659D7A66B80" xlink:to="loc_cmcsa_Notes0.250percentDue2027Member_3FEEC6B8183A8FC4D0BBC659D7A726BA" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_Notes1.500percentDue2029Member" xlink:label="loc_cmcsa_Notes1.500percentDue2029Member_DB048A8A9D20CD64DB2AC659D7A7DFDA" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_7DE9A07153E2D9BF071BC659D7A66B80" xlink:to="loc_cmcsa_Notes1.500percentDue2029Member_DB048A8A9D20CD64DB2AC659D7A7DFDA" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_Notes0.750percentdue2032Member" xlink:label="loc_cmcsa_Notes0.750percentdue2032Member_2798C226A966BFDA5ECAC659D7A77422" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_7DE9A07153E2D9BF071BC659D7A66B80" xlink:to="loc_cmcsa_Notes0.750percentdue2032Member_2798C226A966BFDA5ECAC659D7A77422" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_Notes1.875percentdue2036Member" xlink:label="loc_cmcsa_Notes1.875percentdue2036Member_1690757B0AD84045A9D9C659D7A80E01" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_7DE9A07153E2D9BF071BC659D7A66B80" xlink:to="loc_cmcsa_Notes1.875percentdue2036Member_1690757B0AD84045A9D9C659D7A80E01" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_Notes1.250percentdue2040Member" xlink:label="loc_cmcsa_Notes1.250percentdue2040Member_C0AEC8325713D8037492C659D7A8294B" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_7DE9A07153E2D9BF071BC659D7A66B80" xlink:to="loc_cmcsa_Notes1.250percentdue2040Member_C0AEC8325713D8037492C659D7A8294B" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_GuaranteedNotes9.455PercentDue2022Member" xlink:label="loc_cmcsa_GuaranteedNotes9.455PercentDue2022Member_7AE3248152F001C301C3C659D7A855C4" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_7DE9A07153E2D9BF071BC659D7A66B80" xlink:to="loc_cmcsa_GuaranteedNotes9.455PercentDue2022Member_7AE3248152F001C301C3C659D7A855C4" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_Notes5.50PercentDue2029Member" xlink:label="loc_cmcsa_Notes5.50PercentDue2029Member_D2D95D3EE6A13E78C66DC659D7A8E9BA" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_7DE9A07153E2D9BF071BC659D7A66B80" xlink:to="loc_cmcsa_Notes5.50PercentDue2029Member_D2D95D3EE6A13E78C66DC659D7A8E9BA" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_ExchangeableSubordinatedDebentures2.0PercentDue2029Member" xlink:label="loc_cmcsa_ExchangeableSubordinatedDebentures2.0PercentDue2029Member_DE556DEFBC6D2E1FA617C659D7A85566" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_7DE9A07153E2D9BF071BC659D7A66B80" xlink:to="loc_cmcsa_ExchangeableSubordinatedDebentures2.0PercentDue2029Member_DE556DEFBC6D2E1FA617C659D7A85566" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CommonClassBMember" xlink:label="loc_us-gaap_CommonClassBMember_0431F521943FFCD7A8A4C659D7A966DA" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_7DE9A07153E2D9BF071BC659D7A66B80" xlink:to="loc_us-gaap_CommonClassBMember_0431F521943FFCD7A8A4C659D7A966DA" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_DocumentType" xlink:label="loc_dei_DocumentType_29AE106135F526F85C2AC659D7A9C74F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_DocumentAndEntityInformationLineItems_1F0DF4A2D541D54EFC01C659D7A9A975" xlink:to="loc_dei_DocumentType_29AE106135F526F85C2AC659D7A9C74F" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_DocumentFiscalPeriodFocus" xlink:label="loc_dei_DocumentFiscalPeriodFocus_02167950B3B63C298745C659D7A9A1DA" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_DocumentAndEntityInformationLineItems_1F0DF4A2D541D54EFC01C659D7A9A975" xlink:to="loc_dei_DocumentFiscalPeriodFocus_02167950B3B63C298745C659D7A9A1DA" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_DocumentQuarterlyReport" xlink:label="loc_dei_DocumentQuarterlyReport_F5944D2D88AAE795ED92C659D7A930F3" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_DocumentAndEntityInformationLineItems_1F0DF4A2D541D54EFC01C659D7A9A975" xlink:to="loc_dei_DocumentQuarterlyReport_F5944D2D88AAE795ED92C659D7A930F3" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_DocumentPeriodEndDate" xlink:label="loc_dei_DocumentPeriodEndDate_D9C7776B402C41B0B833C659D7AA8EE6" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_DocumentAndEntityInformationLineItems_1F0DF4A2D541D54EFC01C659D7A9A975" xlink:to="loc_dei_DocumentPeriodEndDate_D9C7776B402C41B0B833C659D7AA8EE6" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_DocumentTransitionReport" xlink:label="loc_dei_DocumentTransitionReport_67DC746CE60CB863186FC659D7AA7A3C" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_DocumentAndEntityInformationLineItems_1F0DF4A2D541D54EFC01C659D7A9A975" xlink:to="loc_dei_DocumentTransitionReport_67DC746CE60CB863186FC659D7AA7A3C" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_AmendmentFlag" xlink:label="loc_dei_AmendmentFlag_BAAFBFCA85A0CCC794DCC659D7AA4F02" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_DocumentAndEntityInformationLineItems_1F0DF4A2D541D54EFC01C659D7A9A975" xlink:to="loc_dei_AmendmentFlag_BAAFBFCA85A0CCC794DCC659D7AA4F02" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_DocumentFiscalYearFocus" xlink:label="loc_dei_DocumentFiscalYearFocus_B67987332FE163305EAAC659D7AACA98" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_DocumentAndEntityInformationLineItems_1F0DF4A2D541D54EFC01C659D7A9A975" xlink:to="loc_dei_DocumentFiscalYearFocus_B67987332FE163305EAAC659D7AACA98" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_CurrentFiscalYearEndDate" xlink:label="loc_dei_CurrentFiscalYearEndDate_498A0A3CF1FAEE97066CC659D7AA3587" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_DocumentAndEntityInformationLineItems_1F0DF4A2D541D54EFC01C659D7A9A975" xlink:to="loc_dei_CurrentFiscalYearEndDate_498A0A3CF1FAEE97066CC659D7AA3587" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityFileNumber" xlink:label="loc_dei_EntityFileNumber_03847EAB83FE9CC9AD42C659D7AA9FC7" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_DocumentAndEntityInformationLineItems_1F0DF4A2D541D54EFC01C659D7A9A975" xlink:to="loc_dei_EntityFileNumber_03847EAB83FE9CC9AD42C659D7AA9FC7" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityRegistrantName" xlink:label="loc_dei_EntityRegistrantName_49282CEBFB1D675F144BC659D7AA14A1" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_DocumentAndEntityInformationLineItems_1F0DF4A2D541D54EFC01C659D7A9A975" xlink:to="loc_dei_EntityRegistrantName_49282CEBFB1D675F144BC659D7AA14A1" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityCentralIndexKey" xlink:label="loc_dei_EntityCentralIndexKey_820A5FBB59313C2A988FC659D7AB175D" xlink:type="locator" />
    <link:definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_DocumentAndEntityInformationLineItems_1F0DF4A2D541D54EFC01C659D7A9A975" xlink:to="loc_dei_EntityCentralIndexKey_820A5FBB59313C2A988FC659D7AB175D" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityTaxIdentificationNumber" xlink:label="loc_dei_EntityTaxIdentificationNumber_839DAA8F32F83A5326DDC659D7AB8078" xlink:type="locator" />
    <link:definitionArc order="12" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_DocumentAndEntityInformationLineItems_1F0DF4A2D541D54EFC01C659D7A9A975" xlink:to="loc_dei_EntityTaxIdentificationNumber_839DAA8F32F83A5326DDC659D7AB8078" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityIncorporationStateCountryCode" xlink:label="loc_dei_EntityIncorporationStateCountryCode_D3D54921035AEE0716F8C659D7ABD908" xlink:type="locator" />
    <link:definitionArc order="13" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_DocumentAndEntityInformationLineItems_1F0DF4A2D541D54EFC01C659D7A9A975" xlink:to="loc_dei_EntityIncorporationStateCountryCode_D3D54921035AEE0716F8C659D7ABD908" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityAddressAddressLine1" xlink:label="loc_dei_EntityAddressAddressLine1_7FB5908B49674528CBE6C659D7ABA4BA" xlink:type="locator" />
    <link:definitionArc order="14" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_DocumentAndEntityInformationLineItems_1F0DF4A2D541D54EFC01C659D7A9A975" xlink:to="loc_dei_EntityAddressAddressLine1_7FB5908B49674528CBE6C659D7ABA4BA" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityAddressCityOrTown" xlink:label="loc_dei_EntityAddressCityOrTown_FDBDB20AA51BEF0D2E23C659D7AB377C" xlink:type="locator" />
    <link:definitionArc order="15" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_DocumentAndEntityInformationLineItems_1F0DF4A2D541D54EFC01C659D7A9A975" xlink:to="loc_dei_EntityAddressCityOrTown_FDBDB20AA51BEF0D2E23C659D7AB377C" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityAddressStateOrProvince" xlink:label="loc_dei_EntityAddressStateOrProvince_A2CB7E4A58384F4D2793C659D7ABF621" xlink:type="locator" />
    <link:definitionArc order="16" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_DocumentAndEntityInformationLineItems_1F0DF4A2D541D54EFC01C659D7A9A975" xlink:to="loc_dei_EntityAddressStateOrProvince_A2CB7E4A58384F4D2793C659D7ABF621" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityAddressPostalZipCode" xlink:label="loc_dei_EntityAddressPostalZipCode_E32FB8C5D0B039B501F1C659D7B1EEF5" xlink:type="locator" />
    <link:definitionArc order="17" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_DocumentAndEntityInformationLineItems_1F0DF4A2D541D54EFC01C659D7A9A975" xlink:to="loc_dei_EntityAddressPostalZipCode_E32FB8C5D0B039B501F1C659D7B1EEF5" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_CityAreaCode" xlink:label="loc_dei_CityAreaCode_B3E96C38231EEED29237C659D7B152D8" xlink:type="locator" />
    <link:definitionArc order="18" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_DocumentAndEntityInformationLineItems_1F0DF4A2D541D54EFC01C659D7A9A975" xlink:to="loc_dei_CityAreaCode_B3E96C38231EEED29237C659D7B152D8" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LocalPhoneNumber" xlink:label="loc_dei_LocalPhoneNumber_F91F59498C757CB834B7C659D7B15091" xlink:type="locator" />
    <link:definitionArc order="19" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_DocumentAndEntityInformationLineItems_1F0DF4A2D541D54EFC01C659D7A9A975" xlink:to="loc_dei_LocalPhoneNumber_F91F59498C757CB834B7C659D7B15091" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_Security12bTitle" xlink:label="loc_dei_Security12bTitle_B87637ACD2D6EC925177C659D7B1F4BC" xlink:type="locator" />
    <link:definitionArc order="20" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_DocumentAndEntityInformationLineItems_1F0DF4A2D541D54EFC01C659D7A9A975" xlink:to="loc_dei_Security12bTitle_B87637ACD2D6EC925177C659D7B1F4BC" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_TradingSymbol" xlink:label="loc_dei_TradingSymbol_6DE2AFC0492D5194742DC659D7B257D2" xlink:type="locator" />
    <link:definitionArc order="21" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_DocumentAndEntityInformationLineItems_1F0DF4A2D541D54EFC01C659D7A9A975" xlink:to="loc_dei_TradingSymbol_6DE2AFC0492D5194742DC659D7B257D2" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_SecurityExchangeName" xlink:label="loc_dei_SecurityExchangeName_A94566100055BD8E9A7EC659D7B217B2" xlink:type="locator" />
    <link:definitionArc order="22" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_DocumentAndEntityInformationLineItems_1F0DF4A2D541D54EFC01C659D7A9A975" xlink:to="loc_dei_SecurityExchangeName_A94566100055BD8E9A7EC659D7B217B2" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityCurrentReportingStatus" xlink:label="loc_dei_EntityCurrentReportingStatus_18199A2F3ECB8A202F95C659D7B2B398" xlink:type="locator" />
    <link:definitionArc order="23" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_DocumentAndEntityInformationLineItems_1F0DF4A2D541D54EFC01C659D7A9A975" xlink:to="loc_dei_EntityCurrentReportingStatus_18199A2F3ECB8A202F95C659D7B2B398" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityInteractiveDataCurrent" xlink:label="loc_dei_EntityInteractiveDataCurrent_DF0605838FF1E72A490AC659D7B26ADF" xlink:type="locator" />
    <link:definitionArc order="24" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_DocumentAndEntityInformationLineItems_1F0DF4A2D541D54EFC01C659D7A9A975" xlink:to="loc_dei_EntityInteractiveDataCurrent_DF0605838FF1E72A490AC659D7B26ADF" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityFilerCategory" xlink:label="loc_dei_EntityFilerCategory_6847253F18FFCDE0A10CC659D7B27DE3" xlink:type="locator" />
    <link:definitionArc order="25" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_DocumentAndEntityInformationLineItems_1F0DF4A2D541D54EFC01C659D7A9A975" xlink:to="loc_dei_EntityFilerCategory_6847253F18FFCDE0A10CC659D7B27DE3" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntitySmallBusiness" xlink:label="loc_dei_EntitySmallBusiness_EAF1A09FDC81BADE2305C659D7B229AF" xlink:type="locator" />
    <link:definitionArc order="26" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_DocumentAndEntityInformationLineItems_1F0DF4A2D541D54EFC01C659D7A9A975" xlink:to="loc_dei_EntitySmallBusiness_EAF1A09FDC81BADE2305C659D7B229AF" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityEmergingGrowthCompany" xlink:label="loc_dei_EntityEmergingGrowthCompany_EF3186D038901809592EC659D7B21676" xlink:type="locator" />
    <link:definitionArc order="27" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_DocumentAndEntityInformationLineItems_1F0DF4A2D541D54EFC01C659D7A9A975" xlink:to="loc_dei_EntityEmergingGrowthCompany_EF3186D038901809592EC659D7B21676" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityShellCompany" xlink:label="loc_dei_EntityShellCompany_90105877D04DCB9D744BC659D7B31FAB" xlink:type="locator" />
    <link:definitionArc order="28" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_DocumentAndEntityInformationLineItems_1F0DF4A2D541D54EFC01C659D7A9A975" xlink:to="loc_dei_EntityShellCompany_90105877D04DCB9D744BC659D7B31FAB" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityCommonStockSharesOutstanding" xlink:label="loc_dei_EntityCommonStockSharesOutstanding_EBC142836608F1391147C659D7B3CC7D" xlink:type="locator" />
    <link:definitionArc order="29" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_DocumentAndEntityInformationLineItems_1F0DF4A2D541D54EFC01C659D7A9A975" xlink:to="loc_dei_EntityCommonStockSharesOutstanding_EBC142836608F1391147C659D7B3CC7D" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/EarningsPerShare" xlink:type="extended" />
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/EarningsPerShareDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/EarningsPerShareTables" xlink:type="extended" />
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/IntangibleAssets" xlink:type="extended" />
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/IntangibleAssetsAmortizationOfIntangibleAssetsDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/IntangibleAssetsSummaryOfIntangibleAssetsDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassLineItems" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassLineItems_3A19153784D5836F7CDFCBCB85B18E1D" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ScheduleOfIndefiniteLivedIntangibleAssetsTable" xlink:label="loc_us-gaap_ScheduleOfIndefiniteLivedIntangibleAssetsTable_F0401ADEF6C1BF94A844CBCB85B092E0" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassLineItems_3A19153784D5836F7CDFCBCB85B18E1D" xlink:to="loc_us-gaap_ScheduleOfIndefiniteLivedIntangibleAssetsTable_F0401ADEF6C1BF94A844CBCB85B092E0" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_F4CEDCAD99837F1D73E0CBCB85B0EACC" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfIndefiniteLivedIntangibleAssetsTable_F0401ADEF6C1BF94A844CBCB85B092E0" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_F4CEDCAD99837F1D73E0CBCB85B0EACC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_CBEDAA171A3DF04FBED3CBCB85B0FED3_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_F4CEDCAD99837F1D73E0CBCB85B0EACC" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_CBEDAA171A3DF04FBED3CBCB85B0FED3_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_CBEDAA171A3DF04FBED3CBCB85B0FED3" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_F4CEDCAD99837F1D73E0CBCB85B0EACC" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_CBEDAA171A3DF04FBED3CBCB85B0FED3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FranchiseRightsMember" xlink:label="loc_us-gaap_FranchiseRightsMember_A94BC11C047A6B8DFF17CBCB85B1080A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_CBEDAA171A3DF04FBED3CBCB85B0FED3" xlink:to="loc_us-gaap_FranchiseRightsMember_A94BC11C047A6B8DFF17CBCB85B1080A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TradeNamesMember" xlink:label="loc_us-gaap_TradeNamesMember_394FEC426EC08014ACF7CBCB85B1CB5F" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_CBEDAA171A3DF04FBED3CBCB85B0FED3" xlink:to="loc_us-gaap_TradeNamesMember_394FEC426EC08014ACF7CBCB85B1CB5F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OperatingAndBroadcastRightsMember" xlink:label="loc_us-gaap_OperatingAndBroadcastRightsMember_AABC5A14D9AEF9429DD2CBCBE0C3233B" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_CBEDAA171A3DF04FBED3CBCB85B0FED3" xlink:to="loc_us-gaap_OperatingAndBroadcastRightsMember_AABC5A14D9AEF9429DD2CBCBE0C3233B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill_8070B205F3C9FFA34086CBCB85B1570E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassLineItems_3A19153784D5836F7CDFCBCB85B18E1D" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill_8070B205F3C9FFA34086CBCB85B1570E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_89AB8BCA7231BADC7A9ECBCB85B36AA3" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_E0506209E34114F5573FCBCB85B26AD6" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_89AB8BCA7231BADC7A9ECBCB85B36AA3" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_E0506209E34114F5573FCBCB85B26AD6" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_43657F041B96B58E345BCBCB85B2C65A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_E0506209E34114F5573FCBCB85B26AD6" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_43657F041B96B58E345BCBCB85B2C65A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_9C0D4D0CF37324D9DD19CBCB85B2A7FF_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_43657F041B96B58E345BCBCB85B2C65A" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_9C0D4D0CF37324D9DD19CBCB85B2A7FF_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_9C0D4D0CF37324D9DD19CBCB85B2A7FF" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_43657F041B96B58E345BCBCB85B2C65A" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_9C0D4D0CF37324D9DD19CBCB85B2A7FF" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CustomerRelationshipsMember" xlink:label="loc_us-gaap_CustomerRelationshipsMember_E316EF035D6E8D3C890CCBCB85B3F163" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_9C0D4D0CF37324D9DD19CBCB85B2A7FF" xlink:to="loc_us-gaap_CustomerRelationshipsMember_E316EF035D6E8D3C890CCBCB85B3F163" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ComputerSoftwareIntangibleAssetMember" xlink:label="loc_us-gaap_ComputerSoftwareIntangibleAssetMember_F6385DE726AA78C74FD1CBCB85B38285" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_9C0D4D0CF37324D9DD19CBCB85B2A7FF" xlink:to="loc_us-gaap_ComputerSoftwareIntangibleAssetMember_F6385DE726AA78C74FD1CBCB85B38285" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OtherIntangibleAssetsMember" xlink:label="loc_us-gaap_OtherIntangibleAssetsMember_AFC3B1B44646A823D51DCBCB85B3FBE1" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_9C0D4D0CF37324D9DD19CBCB85B2A7FF" xlink:to="loc_us-gaap_OtherIntangibleAssetsMember_AFC3B1B44646A823D51DCBCB85B3FBE1" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetUsefulLife" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_1336C7EAB5F02F388EA6CBCB85B328B1" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_89AB8BCA7231BADC7A9ECBCB85B36AA3" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_1336C7EAB5F02F388EA6CBCB85B328B1" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsGross" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsGross_EF091795588793BB9E63CBCB85B41BB3" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_89AB8BCA7231BADC7A9ECBCB85B36AA3" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsGross_EF091795588793BB9E63CBCB85B41BB3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_3CB9228A0936F81F7710CBCB85B414AF" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_89AB8BCA7231BADC7A9ECBCB85B36AA3" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_3CB9228A0936F81F7710CBCB85B414AF" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/IntangibleAssetsTables" xlink:type="extended" />
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/Investments" xlink:type="extended" />
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/InvestmentsEquityMethodInvestmentsDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ScheduleOfEquityMethodInvestmentsLineItems" xlink:label="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_21E0373ED59C33CB31DAC34743AC2EBC" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ScheduleOfEquityMethodInvestmentsTable" xlink:label="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_E144A51ED37BABB8158CC34743A7BA5B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_21E0373ED59C33CB31DAC34743AC2EBC" xlink:to="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_E144A51ED37BABB8158CC34743A7BA5B" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_38B7A7872099E3438A84C34743A9B374" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_E144A51ED37BABB8158CC34743A7BA5B" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_38B7A7872099E3438A84C34743A9B374" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_AF3D0B0693037502BA7DC34743A9758C_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_38B7A7872099E3438A84C34743A9B374" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_AF3D0B0693037502BA7DC34743A9758C_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_AF3D0B0693037502BA7DC34743A9758C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_38B7A7872099E3438A84C34743A9B374" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_AF3D0B0693037502BA7DC34743A9758C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueInputsLevel2Member" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_B01509AD0BB856D1A710C34743A915FD" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_AF3D0B0693037502BA7DC34743A9758C" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_B01509AD0BB856D1A710C34743A915FD" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis" xlink:label="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_BA47DE8DC44A4BA379E8C34743AA6430" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_E144A51ED37BABB8158CC34743A7BA5B" xlink:to="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_BA47DE8DC44A4BA379E8C34743AA6430" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_EquityMethodInvesteeNameDomain" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_94246A084EEAD0703869C34743AA5715_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_BA47DE8DC44A4BA379E8C34743AA6430" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_94246A084EEAD0703869C34743AA5715_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_EquityMethodInvesteeNameDomain" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_94246A084EEAD0703869C34743AA5715" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_BA47DE8DC44A4BA379E8C34743AA6430" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_94246A084EEAD0703869C34743AA5715" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_AtairosMember" xlink:label="loc_cmcsa_AtairosMember_FB93B8158D2296A27008C34743AB00ED" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_94246A084EEAD0703869C34743AA5715" xlink:to="loc_cmcsa_AtairosMember_FB93B8158D2296A27008C34743AB00ED" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_HuluMember" xlink:label="loc_cmcsa_HuluMember_5E0236AE016F709F642CC34743AB5F29" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_94246A084EEAD0703869C34743AA5715" xlink:to="loc_cmcsa_HuluMember_5E0236AE016F709F642CC34743AB5F29" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_CounterpartyNameAxis" xlink:label="loc_srt_CounterpartyNameAxis_FB248F36E5022A4AF13FC34743ABD371" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_E144A51ED37BABB8158CC34743A7BA5B" xlink:to="loc_srt_CounterpartyNameAxis_FB248F36E5022A4AF13FC34743ABD371" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_1B54305122BF6163FD64C34743AC89F4_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_FB248F36E5022A4AF13FC34743ABD371" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_1B54305122BF6163FD64C34743AC89F4_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_1B54305122BF6163FD64C34743AC89F4" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_FB248F36E5022A4AF13FC34743ABD371" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_1B54305122BF6163FD64C34743AC89F4" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_AtairosMember" xlink:label="loc_cmcsa_AtairosMember_F4EBDC02507B4B2EC0F1C34743ACF393" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_1B54305122BF6163FD64C34743AC89F4" xlink:to="loc_cmcsa_AtairosMember_F4EBDC02507B4B2EC0F1C34743ACF393" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_IncomeLossFromEquityMethodInvestments" xlink:label="loc_us-gaap_IncomeLossFromEquityMethodInvestments_36C985446FE2F51923D2C34743ACD213" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_21E0373ED59C33CB31DAC34743AC2EBC" xlink:to="loc_us-gaap_IncomeLossFromEquityMethodInvestments_36C985446FE2F51923D2C34743ACD213" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_CapitalContributionToVIE" xlink:label="loc_cmcsa_CapitalContributionToVIE_910B20C34D7C9273253FC34743ADBED7" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_21E0373ED59C33CB31DAC34743AC2EBC" xlink:to="loc_cmcsa_CapitalContributionToVIE_910B20C34D7C9273253FC34743ADBED7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_EquityMethodInvestments" xlink:label="loc_us-gaap_EquityMethodInvestments_D465D23DBC7213D0EAE8C34743AD505F" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_21E0373ED59C33CB31DAC34743AC2EBC" xlink:to="loc_us-gaap_EquityMethodInvestments_D465D23DBC7213D0EAE8C34743AD505F" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_DeferredGainRecognizedOnDilutionOfEquityMethodInvestment" xlink:label="loc_cmcsa_DeferredGainRecognizedOnDilutionOfEquityMethodInvestment_2785A8384FAD748D41A4C34743AD2CD7" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_21E0373ED59C33CB31DAC34743AC2EBC" xlink:to="loc_cmcsa_DeferredGainRecognizedOnDilutionOfEquityMethodInvestment_2785A8384FAD748D41A4C34743AD2CD7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PaymentsToAcquireEquityMethodInvestments" xlink:label="loc_us-gaap_PaymentsToAcquireEquityMethodInvestments_CA53E009A61531D0BA57C34743ADD736" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_21E0373ED59C33CB31DAC34743AC2EBC" xlink:to="loc_us-gaap_PaymentsToAcquireEquityMethodInvestments_CA53E009A61531D0BA57C34743ADD736" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_InvestmentSecuringCollateralizedObligation" xlink:label="loc_cmcsa_InvestmentSecuringCollateralizedObligation_D73FC1EF31E9579AC856C34743ADA2B9" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_21E0373ED59C33CB31DAC34743AC2EBC" xlink:to="loc_cmcsa_InvestmentSecuringCollateralizedObligation_D73FC1EF31E9579AC856C34743ADA2B9" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_ProceedsFromCollateralizedObligation" xlink:label="loc_cmcsa_ProceedsFromCollateralizedObligation_1CA149D468C3A8F880D3C34743AE0DD5" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_21E0373ED59C33CB31DAC34743AC2EBC" xlink:to="loc_cmcsa_ProceedsFromCollateralizedObligation_1CA149D468C3A8F880D3C34743AE0DD5" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_CollateralizedObligation" xlink:label="loc_cmcsa_CollateralizedObligation_A41D74EDAF335D66FB7BC34743AEDABC" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_21E0373ED59C33CB31DAC34743AC2EBC" xlink:to="loc_cmcsa_CollateralizedObligation_A41D74EDAF335D66FB7BC34743AEDABC" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_CollateralizedObligationFairValue" xlink:label="loc_cmcsa_CollateralizedObligationFairValue_F92CB1103B7CF6B976A7C34743AEDB20" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_21E0373ED59C33CB31DAC34743AC2EBC" xlink:to="loc_cmcsa_CollateralizedObligationFairValue_F92CB1103B7CF6B976A7C34743AEDB20" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/InvestmentsInvestmentAndOtherIncomeLossNetDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/InvestmentsMarketableEquitySecuritiesDetails" xlink:type="extended">
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_ScheduleofFairValueMethodInvestmentsLineItems" xlink:label="loc_cmcsa_ScheduleofFairValueMethodInvestmentsLineItems_E9074CC357BEB87AECB0AD509594339E" xlink:type="locator" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_ScheduleofFairValueMethodInvestmentsTable" xlink:label="loc_cmcsa_ScheduleofFairValueMethodInvestmentsTable_6071635C513F3B18F6BCAD50958F7551" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_cmcsa_ScheduleofFairValueMethodInvestmentsLineItems_E9074CC357BEB87AECB0AD509594339E" xlink:to="loc_cmcsa_ScheduleofFairValueMethodInvestmentsTable_6071635C513F3B18F6BCAD50958F7551" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis" xlink:label="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_6B09620116DE57E49303AD50959019FC" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_cmcsa_ScheduleofFairValueMethodInvestmentsTable_6071635C513F3B18F6BCAD50958F7551" xlink:to="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_6B09620116DE57E49303AD50959019FC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_EquityMethodInvesteeNameDomain" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_3910395A4A503E0DEF75AD50959053A0_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_6B09620116DE57E49303AD50959019FC" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_3910395A4A503E0DEF75AD50959053A0_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_EquityMethodInvesteeNameDomain" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_3910395A4A503E0DEF75AD50959053A0" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_6B09620116DE57E49303AD50959019FC" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_3910395A4A503E0DEF75AD50959053A0" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_PelotonMember" xlink:label="loc_cmcsa_PelotonMember_F3D9D294E52725E2D385AD509591500B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_3910395A4A503E0DEF75AD50959053A0" xlink:to="loc_cmcsa_PelotonMember_F3D9D294E52725E2D385AD509591500B" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_SnapMember" xlink:label="loc_cmcsa_SnapMember_7795F15A48E99A3EBBE3AD5095937DB6" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_3910395A4A503E0DEF75AD50959053A0" xlink:to="loc_cmcsa_SnapMember_7795F15A48E99A3EBBE3AD5095937DB6" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_EquitySecuritiesFvNiGainLoss" xlink:label="loc_us-gaap_EquitySecuritiesFvNiGainLoss_46B3B9B4AA3C42087865AD50959417AB" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_ScheduleofFairValueMethodInvestmentsLineItems_E9074CC357BEB87AECB0AD509594339E" xlink:to="loc_us-gaap_EquitySecuritiesFvNiGainLoss_46B3B9B4AA3C42087865AD50959417AB" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_EquitySecuritiesFvNi" xlink:label="loc_us-gaap_EquitySecuritiesFvNi_F87AD883EA4AB461C3B8AD5095948935" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_ScheduleofFairValueMethodInvestmentsLineItems_E9074CC357BEB87AECB0AD509594339E" xlink:to="loc_us-gaap_EquitySecuritiesFvNi_F87AD883EA4AB461C3B8AD5095948935" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_EquitySecuritiesFvNiUnrealizedGainLoss" xlink:label="loc_us-gaap_EquitySecuritiesFvNiUnrealizedGainLoss_7F89C2F586965D4B2857AD5095947EA5" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_cmcsa_ScheduleofFairValueMethodInvestmentsLineItems_E9074CC357BEB87AECB0AD509594339E" xlink:to="loc_us-gaap_EquitySecuritiesFvNiUnrealizedGainLoss_7F89C2F586965D4B2857AD5095947EA5" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/InvestmentsOtherInvestmentsDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ScheduleOfHeldToMaturitySecuritiesLineItems" xlink:label="loc_us-gaap_ScheduleOfHeldToMaturitySecuritiesLineItems_EFDC52851857C266CE12C353CD05D5EC" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_InvestmentHoldingsTable" xlink:label="loc_us-gaap_InvestmentHoldingsTable_C9C01A0AC06677D28A7AC353CCFB3101" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfHeldToMaturitySecuritiesLineItems_EFDC52851857C266CE12C353CD05D5EC" xlink:to="loc_us-gaap_InvestmentHoldingsTable_C9C01A0AC06677D28A7AC353CCFB3101" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis" xlink:label="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_04AD7E09C1E8E4C6A82AC353CCFCA5B5" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_InvestmentHoldingsTable_C9C01A0AC06677D28A7AC353CCFB3101" xlink:to="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_04AD7E09C1E8E4C6A82AC353CCFCA5B5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_EquityMethodInvesteeNameDomain" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_53B1CB2B6BE1DC7D77EAC353CCFD2006_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_04AD7E09C1E8E4C6A82AC353CCFCA5B5" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_53B1CB2B6BE1DC7D77EAC353CCFD2006_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_EquityMethodInvesteeNameDomain" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_53B1CB2B6BE1DC7D77EAC353CCFD2006" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_04AD7E09C1E8E4C6A82AC353CCFCA5B5" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_53B1CB2B6BE1DC7D77EAC353CCFD2006" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_AirTouchMember" xlink:label="loc_cmcsa_AirTouchMember_07466101E05FACCB25F1C353CCFDA4CD" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_53B1CB2B6BE1DC7D77EAC353CCFD2006" xlink:to="loc_cmcsa_AirTouchMember_07466101E05FACCB25F1C353CCFDA4CD" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_37DB3224D4E976EBEE36C353CCFDC6F9" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_InvestmentHoldingsTable_C9C01A0AC06677D28A7AC353CCFB3101" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_37DB3224D4E976EBEE36C353CCFDC6F9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_C873A32AA9E57359445EC353CCFE1344_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_37DB3224D4E976EBEE36C353CCFDC6F9" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_C873A32AA9E57359445EC353CCFE1344_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_C873A32AA9E57359445EC353CCFE1344" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_37DB3224D4E976EBEE36C353CCFDC6F9" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_C873A32AA9E57359445EC353CCFE1344" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueInputsLevel2Member" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_6F44703D0E8150403718C353CCFE2D57" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_C873A32AA9E57359445EC353CCFE1344" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_6F44703D0E8150403718C353CCFE2D57" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_711D8F6C03EFBACBB5E5C353CCFE90D2" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_InvestmentHoldingsTable_C9C01A0AC06677D28A7AC353CCFB3101" xlink:to="loc_dei_LegalEntityAxis_711D8F6C03EFBACBB5E5C353CCFE90D2" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_824E0B78FC7B8579DF5DC353CCFF1427_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_711D8F6C03EFBACBB5E5C353CCFE90D2" xlink:to="loc_dei_EntityDomain_824E0B78FC7B8579DF5DC353CCFF1427_default" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_824E0B78FC7B8579DF5DC353CCFF1427" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_711D8F6C03EFBACBB5E5C353CCFE90D2" xlink:to="loc_dei_EntityDomain_824E0B78FC7B8579DF5DC353CCFF1427" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_AirTouchMember" xlink:label="loc_cmcsa_AirTouchMember_D538841624027CFEF471C353CCFFA681" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_824E0B78FC7B8579DF5DC353CCFF1427" xlink:to="loc_cmcsa_AirTouchMember_D538841624027CFEF471C353CCFFA681" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SubsequentEventTypeAxis" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_20C515A17948B8CD938FC353CCFF9A05" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_InvestmentHoldingsTable_C9C01A0AC06677D28A7AC353CCFB3101" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_20C515A17948B8CD938FC353CCFF9A05" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_DFA0E657830BA3796F88C353CD00217A_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_20C515A17948B8CD938FC353CCFF9A05" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_DFA0E657830BA3796F88C353CD00217A_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_DFA0E657830BA3796F88C353CD00217A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_20C515A17948B8CD938FC353CCFF9A05" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_DFA0E657830BA3796F88C353CD00217A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SubsequentEventMember" xlink:label="loc_us-gaap_SubsequentEventMember_8ED272E366FE254A90E5C353CD052300" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_DFA0E657830BA3796F88C353CD00217A" xlink:to="loc_us-gaap_SubsequentEventMember_8ED272E366FE254A90E5C353CD052300" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_NumberofPreferredStockSeries" xlink:label="loc_cmcsa_NumberofPreferredStockSeries_502A07E9A0DAFFB200C2C353CD0629A2" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfHeldToMaturitySecuritiesLineItems_EFDC52851857C266CE12C353CD05D5EC" xlink:to="loc_cmcsa_NumberofPreferredStockSeries_502A07E9A0DAFFB200C2C353CD0629A2" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_HeldToMaturitySecuritiesCurrent" xlink:label="loc_us-gaap_HeldToMaturitySecuritiesCurrent_67C4A4016105B5707A3EC353CD0610C9" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfHeldToMaturitySecuritiesLineItems_EFDC52851857C266CE12C353CD05D5EC" xlink:to="loc_us-gaap_HeldToMaturitySecuritiesCurrent_67C4A4016105B5707A3EC353CD0610C9" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_CarryingAmountOfRedeemablePreferredStock" xlink:label="loc_cmcsa_CarryingAmountOfRedeemablePreferredStock_4C77B59B3482198E4172C353CD078271" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfHeldToMaturitySecuritiesLineItems_EFDC52851857C266CE12C353CD05D5EC" xlink:to="loc_cmcsa_CarryingAmountOfRedeemablePreferredStock_4C77B59B3482198E4172C353CD078271" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ProceedsFromMaturitiesPrepaymentsAndCallsOfHeldToMaturitySecurities" xlink:label="loc_us-gaap_ProceedsFromMaturitiesPrepaymentsAndCallsOfHeldToMaturitySecurities_831746BB0667386F3E1AC353CD070D35" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfHeldToMaturitySecuritiesLineItems_EFDC52851857C266CE12C353CD05D5EC" xlink:to="loc_us-gaap_ProceedsFromMaturitiesPrepaymentsAndCallsOfHeldToMaturitySecurities_831746BB0667386F3E1AC353CD070D35" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_PaymentsForRepurchaseandRedemptionofSubsidiaryPreferredStock" xlink:label="loc_cmcsa_PaymentsForRepurchaseandRedemptionofSubsidiaryPreferredStock_5C7E6873976CF2891B09C353CD07758A" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfHeldToMaturitySecuritiesLineItems_EFDC52851857C266CE12C353CD05D5EC" xlink:to="loc_cmcsa_PaymentsForRepurchaseandRedemptionofSubsidiaryPreferredStock_5C7E6873976CF2891B09C353CD07758A" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/InvestmentsScheduleOfInvestmentsDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/InvestmentsTables" xlink:type="extended" />
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/LongTermDebt" xlink:type="extended" />
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/LongTermDebtNarrativeDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DebtInstrumentLineItems" xlink:label="loc_us-gaap_DebtInstrumentLineItems_1E3896509057A0EB420BC35608C2D0AA" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DebtInstrumentTable" xlink:label="loc_us-gaap_DebtInstrumentTable_68458D88F4F50EE40D45C35608BFB2BC" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_1E3896509057A0EB420BC35608C2D0AA" xlink:to="loc_us-gaap_DebtInstrumentTable_68458D88F4F50EE40D45C35608BFB2BC" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DebtInstrumentAxis" xlink:label="loc_us-gaap_DebtInstrumentAxis_241CCE0670BF810069DEC35608C0EBC3" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_68458D88F4F50EE40D45C35608BFB2BC" xlink:to="loc_us-gaap_DebtInstrumentAxis_241CCE0670BF810069DEC35608C0EBC3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_5AEB8BD4F07FE3681784C35608C02779_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_241CCE0670BF810069DEC35608C0EBC3" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_5AEB8BD4F07FE3681784C35608C02779_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_5AEB8BD4F07FE3681784C35608C02779" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_241CCE0670BF810069DEC35608C0EBC3" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_5AEB8BD4F07FE3681784C35608C02779" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_SkySeniorNotesDue2020Member" xlink:label="loc_cmcsa_SkySeniorNotesDue2020Member_F0E5947156731D6E8E45C35608C00A2F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_5AEB8BD4F07FE3681784C35608C02779" xlink:to="loc_cmcsa_SkySeniorNotesDue2020Member_F0E5947156731D6E8E45C35608C00A2F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LongtermDebtTypeAxis" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_2D5294947D51BAFEBDA8C35608C05321" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_68458D88F4F50EE40D45C35608BFB2BC" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_2D5294947D51BAFEBDA8C35608C05321" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LongtermDebtTypeDomain" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_5AB3349C6010DA8D9939C35608C11FBA_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_2D5294947D51BAFEBDA8C35608C05321" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_5AB3349C6010DA8D9939C35608C11FBA_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LongtermDebtTypeDomain" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_5AB3349C6010DA8D9939C35608C11FBA" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_2D5294947D51BAFEBDA8C35608C05321" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_5AB3349C6010DA8D9939C35608C11FBA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SeniorNotesMember" xlink:label="loc_us-gaap_SeniorNotesMember_4323C8DF8402385965BBC35608C12A84" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_5AB3349C6010DA8D9939C35608C11FBA" xlink:to="loc_us-gaap_SeniorNotesMember_4323C8DF8402385965BBC35608C12A84" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SubsequentEventTypeAxis" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_D0DA7D5E9F0A34D9AB2BC35608C11D84" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_68458D88F4F50EE40D45C35608BFB2BC" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_D0DA7D5E9F0A34D9AB2BC35608C11D84" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_6C001193BFB748D16FF6C35608C19E93_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_D0DA7D5E9F0A34D9AB2BC35608C11D84" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_6C001193BFB748D16FF6C35608C19E93_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_6C001193BFB748D16FF6C35608C19E93" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_D0DA7D5E9F0A34D9AB2BC35608C11D84" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_6C001193BFB748D16FF6C35608C19E93" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SubsequentEventMember" xlink:label="loc_us-gaap_SubsequentEventMember_997D9C42E6AF8DFDAFFEC35608C222C0" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_6C001193BFB748D16FF6C35608C19E93" xlink:to="loc_us-gaap_SubsequentEventMember_997D9C42E6AF8DFDAFFEC35608C222C0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DebtAndCapitalLeaseObligations" xlink:label="loc_us-gaap_DebtAndCapitalLeaseObligations_2CEA82E0C10B9140DCA8C35608C2C03D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_1E3896509057A0EB420BC35608C2D0AA" xlink:to="loc_us-gaap_DebtAndCapitalLeaseObligations_2CEA82E0C10B9140DCA8C35608C2C03D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LongTermDebtFairValue" xlink:label="loc_us-gaap_LongTermDebtFairValue_920AA947C08FF349D09FC35608C3A393" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_1E3896509057A0EB420BC35608C2D0AA" xlink:to="loc_us-gaap_LongTermDebtFairValue_920AA947C08FF349D09FC35608C3A393" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_RepaymentsOfOtherDebt" xlink:label="loc_us-gaap_RepaymentsOfOtherDebt_C5ADA1EB932BA7F68424C35608C39EB4" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_1E3896509057A0EB420BC35608C2D0AA" xlink:to="loc_us-gaap_RepaymentsOfOtherDebt_C5ADA1EB932BA7F68424C35608C39EB4" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/ProgrammingAndProductionCosts" xlink:type="extended" />
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/ProgrammingAndProductionCostsCapitalizedFilmAndTelevisionCostsAndProgrammingRightsDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/ProgrammingAndProductionCostsEstimatedFutureAmortizationExpenseForCapitalizedFilmAndTelevisionCostsAndProgrammingRightsDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/ProgrammingAndProductionCostsRecognizedProgrammingAndProductionCostsDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/ProgrammingAndProductionCostsTables" xlink:type="extended" />
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/RecentAccountingPronouncements" xlink:type="extended" />
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/RecentAccountingPronouncementsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems" xlink:label="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems_ED1C5DCFB6ECF56A522FAD5096080BB9" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable" xlink:label="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable_6D40D847790DA5311B2BAD5096056FCA" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems_ED1C5DCFB6ECF56A522FAD5096080BB9" xlink:to="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable_6D40D847790DA5311B2BAD5096056FCA" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AdjustmentsForNewAccountingPronouncementsAxis" xlink:label="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_6380AC7D6E550F3302F0AD509606FC70" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable_6D40D847790DA5311B2BAD5096056FCA" xlink:to="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_6380AC7D6E550F3302F0AD509606FC70" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TypeOfAdoptionMember" xlink:label="loc_us-gaap_TypeOfAdoptionMember_7FB9B6FAE85A5FB6A36BAD5096062488_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_6380AC7D6E550F3302F0AD509606FC70" xlink:to="loc_us-gaap_TypeOfAdoptionMember_7FB9B6FAE85A5FB6A36BAD5096062488_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TypeOfAdoptionMember" xlink:label="loc_us-gaap_TypeOfAdoptionMember_7FB9B6FAE85A5FB6A36BAD5096062488" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_6380AC7D6E550F3302F0AD509606FC70" xlink:to="loc_us-gaap_TypeOfAdoptionMember_7FB9B6FAE85A5FB6A36BAD5096062488" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AccountingStandardsUpdate201613Member" xlink:label="loc_us-gaap_AccountingStandardsUpdate201613Member_6EF019C8CC63B84BD3C5AD509606F2FD" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfAdoptionMember_7FB9B6FAE85A5FB6A36BAD5096062488" xlink:to="loc_us-gaap_AccountingStandardsUpdate201613Member_6EF019C8CC63B84BD3C5AD509606F2FD" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_C2F2399A52C0FD9368BBAD509607F031" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable_6D40D847790DA5311B2BAD5096056FCA" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_C2F2399A52C0FD9368BBAD509607F031" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaap_EquityComponentDomain_FACA7FF48CB9338A7270AD5096074F48_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_C2F2399A52C0FD9368BBAD509607F031" xlink:to="loc_us-gaap_EquityComponentDomain_FACA7FF48CB9338A7270AD5096074F48_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaap_EquityComponentDomain_FACA7FF48CB9338A7270AD5096074F48" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_C2F2399A52C0FD9368BBAD509607F031" xlink:to="loc_us-gaap_EquityComponentDomain_FACA7FF48CB9338A7270AD5096074F48" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_RetainedEarningsMember" xlink:label="loc_us-gaap_RetainedEarningsMember_4D761D906F9E853492C3AD5096071448" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_FACA7FF48CB9338A7270AD5096074F48" xlink:to="loc_us-gaap_RetainedEarningsMember_4D761D906F9E853492C3AD5096071448" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption" xlink:label="loc_us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption_D3B5F384102A3AAA7F7EAD5096082457" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems_ED1C5DCFB6ECF56A522FAD5096080BB9" xlink:to="loc_us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption_D3B5F384102A3AAA7F7EAD5096082457" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/RecentAccountingPronouncementsPolicies" xlink:type="extended" />
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/Revenue" xlink:type="extended" />
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/RevenueCondensedConsolidatedBalanceSheetDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/RevenueDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DisaggregationOfRevenueLineItems" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_B58649A6D502285438C8C8A25CC88CD3" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DisaggregationOfRevenueTable" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_ED2EE2173F942D8F99E2C8A25CC282D9" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_B58649A6D502285438C8C8A25CC88CD3" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_ED2EE2173F942D8F99E2C8A25CC282D9" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_ConsolidationItemsAxis" xlink:label="loc_srt_ConsolidationItemsAxis_5FD1C6EE013116DDA0AFC8A25CC2B461" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_ED2EE2173F942D8F99E2C8A25CC282D9" xlink:to="loc_srt_ConsolidationItemsAxis_5FD1C6EE013116DDA0AFC8A25CC2B461" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_ConsolidationItemsDomain" xlink:label="loc_srt_ConsolidationItemsDomain_81E489FE9BC21B8395D6C8A25CC3FADE_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_5FD1C6EE013116DDA0AFC8A25CC2B461" xlink:to="loc_srt_ConsolidationItemsDomain_81E489FE9BC21B8395D6C8A25CC3FADE_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_ConsolidationItemsDomain" xlink:label="loc_srt_ConsolidationItemsDomain_81E489FE9BC21B8395D6C8A25CC3FADE" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_5FD1C6EE013116DDA0AFC8A25CC2B461" xlink:to="loc_srt_ConsolidationItemsDomain_81E489FE9BC21B8395D6C8A25CC3FADE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OperatingSegmentsMember" xlink:label="loc_us-gaap_OperatingSegmentsMember_D30543354B49324D00F4C8A25CC37679" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_81E489FE9BC21B8395D6C8A25CC3FADE" xlink:to="loc_us-gaap_OperatingSegmentsMember_D30543354B49324D00F4C8A25CC37679" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CorporateNonSegmentMember" xlink:label="loc_us-gaap_CorporateNonSegmentMember_76CAE6DDCBEF5A7BB771C8A25CC305FF" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_81E489FE9BC21B8395D6C8A25CC3FADE" xlink:to="loc_us-gaap_CorporateNonSegmentMember_76CAE6DDCBEF5A7BB771C8A25CC305FF" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_MaterialReconcilingItemsMember" xlink:label="loc_us-gaap_MaterialReconcilingItemsMember_2BA852AD12B31C0E6DF6C8A25CC477E3" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_81E489FE9BC21B8395D6C8A25CC3FADE" xlink:to="loc_us-gaap_MaterialReconcilingItemsMember_2BA852AD12B31C0E6DF6C8A25CC477E3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementBusinessSegmentsAxis" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_FA6C894D316AFBA4F8F1C8A25CC4FE6F" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_ED2EE2173F942D8F99E2C8A25CC282D9" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_FA6C894D316AFBA4F8F1C8A25CC4FE6F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SegmentDomain" xlink:label="loc_us-gaap_SegmentDomain_83E5DA71D92047384EC2C8A25CC41556_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_FA6C894D316AFBA4F8F1C8A25CC4FE6F" xlink:to="loc_us-gaap_SegmentDomain_83E5DA71D92047384EC2C8A25CC41556_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SegmentDomain" xlink:label="loc_us-gaap_SegmentDomain_83E5DA71D92047384EC2C8A25CC41556" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_FA6C894D316AFBA4F8F1C8A25CC4FE6F" xlink:to="loc_us-gaap_SegmentDomain_83E5DA71D92047384EC2C8A25CC41556" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_CableCommunicationsMember" xlink:label="loc_cmcsa_CableCommunicationsMember_7367796F04EEEA935A10C8A25CC469F5" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_83E5DA71D92047384EC2C8A25CC41556" xlink:to="loc_cmcsa_CableCommunicationsMember_7367796F04EEEA935A10C8A25CC469F5" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_CableNetworksMember" xlink:label="loc_cmcsa_CableNetworksMember_7AC78DE71733A194DA47C8A25CC40F6A" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_83E5DA71D92047384EC2C8A25CC41556" xlink:to="loc_cmcsa_CableNetworksMember_7AC78DE71733A194DA47C8A25CC40F6A" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_BroadcastTelevisionMember" xlink:label="loc_cmcsa_BroadcastTelevisionMember_C0483FD78A17428018E5C8A25CC41492" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_83E5DA71D92047384EC2C8A25CC41556" xlink:to="loc_cmcsa_BroadcastTelevisionMember_C0483FD78A17428018E5C8A25CC41492" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_FilmedEntertainmentMember" xlink:label="loc_cmcsa_FilmedEntertainmentMember_CDC598A12C377C69A38FC8A25CC580FE" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_83E5DA71D92047384EC2C8A25CC41556" xlink:to="loc_cmcsa_FilmedEntertainmentMember_CDC598A12C377C69A38FC8A25CC580FE" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_ThemeParksMember" xlink:label="loc_cmcsa_ThemeParksMember_F84E36D8957B1A527680C8A25CC570B9" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_83E5DA71D92047384EC2C8A25CC41556" xlink:to="loc_cmcsa_ThemeParksMember_F84E36D8957B1A527680C8A25CC570B9" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_NBCUniversalSegmentsMember" xlink:label="loc_cmcsa_NBCUniversalSegmentsMember_1636B5DBFB6BC8DC5EA2C8A25CC5D516" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_83E5DA71D92047384EC2C8A25CC41556" xlink:to="loc_cmcsa_NBCUniversalSegmentsMember_1636B5DBFB6BC8DC5EA2C8A25CC5D516" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_SkyLimitedMember" xlink:label="loc_cmcsa_SkyLimitedMember_3DD1D8F76E09E8B94F86C8A25CC55A09" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_83E5DA71D92047384EC2C8A25CC41556" xlink:to="loc_cmcsa_SkyLimitedMember_3DD1D8F76E09E8B94F86C8A25CC55A09" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_ProductOrServiceAxis" xlink:label="loc_srt_ProductOrServiceAxis_D349C9D917D5415A41EAC8A25CC5C0BB" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_ED2EE2173F942D8F99E2C8A25CC282D9" xlink:to="loc_srt_ProductOrServiceAxis_D349C9D917D5415A41EAC8A25CC5C0BB" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_ProductsAndServicesDomain" xlink:label="loc_srt_ProductsAndServicesDomain_CFBFB52085A6B8ED9751C8A25CC51571_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_D349C9D917D5415A41EAC8A25CC5C0BB" xlink:to="loc_srt_ProductsAndServicesDomain_CFBFB52085A6B8ED9751C8A25CC51571_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_ProductsAndServicesDomain" xlink:label="loc_srt_ProductsAndServicesDomain_CFBFB52085A6B8ED9751C8A25CC51571" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_D349C9D917D5415A41EAC8A25CC5C0BB" xlink:to="loc_srt_ProductsAndServicesDomain_CFBFB52085A6B8ED9751C8A25CC51571" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_ResidentialHighSpeedInternetMember" xlink:label="loc_cmcsa_ResidentialHighSpeedInternetMember_85E9AEBD9442EC7D397AC8A25CC63890" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_CFBFB52085A6B8ED9751C8A25CC51571" xlink:to="loc_cmcsa_ResidentialHighSpeedInternetMember_85E9AEBD9442EC7D397AC8A25CC63890" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_ResidentialVideoMember" xlink:label="loc_cmcsa_ResidentialVideoMember_D2319D69B9BB70AD7C24C8A25CC6F4C2" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_CFBFB52085A6B8ED9751C8A25CC51571" xlink:to="loc_cmcsa_ResidentialVideoMember_D2319D69B9BB70AD7C24C8A25CC6F4C2" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_ResidentialVoiceMember" xlink:label="loc_cmcsa_ResidentialVoiceMember_AB5C532E15100652A5C5C8A25CC62A60" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_CFBFB52085A6B8ED9751C8A25CC51571" xlink:to="loc_cmcsa_ResidentialVoiceMember_AB5C532E15100652A5C5C8A25CC62A60" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_ResidentialWirelessMember" xlink:label="loc_cmcsa_ResidentialWirelessMember_8896BD2EFD74E18CBE59C8A25CC6A6AE" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_CFBFB52085A6B8ED9751C8A25CC51571" xlink:to="loc_cmcsa_ResidentialWirelessMember_8896BD2EFD74E18CBE59C8A25CC6A6AE" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_BusinessServicesMember" xlink:label="loc_cmcsa_BusinessServicesMember_A144F3980A86BAE25C02C8A25CC6710B" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_CFBFB52085A6B8ED9751C8A25CC51571" xlink:to="loc_cmcsa_BusinessServicesMember_A144F3980A86BAE25C02C8A25CC6710B" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_DirectToConsumerMember" xlink:label="loc_cmcsa_DirectToConsumerMember_08EFD8FC7F65665E6243C8A25CC6D2C2" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_CFBFB52085A6B8ED9751C8A25CC51571" xlink:to="loc_cmcsa_DirectToConsumerMember_08EFD8FC7F65665E6243C8A25CC6D2C2" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_DistributionMember" xlink:label="loc_cmcsa_DistributionMember_16ADFDEF4BE99777DA88C8A25CC7B3C7" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_CFBFB52085A6B8ED9751C8A25CC51571" xlink:to="loc_cmcsa_DistributionMember_16ADFDEF4BE99777DA88C8A25CC7B3C7" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_ContentMember" xlink:label="loc_cmcsa_ContentMember_0B02F7D2C0C4E8F77501C8A25CC7363D" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_CFBFB52085A6B8ED9751C8A25CC51571" xlink:to="loc_cmcsa_ContentMember_0B02F7D2C0C4E8F77501C8A25CC7363D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AdvertisingMember" xlink:label="loc_us-gaap_AdvertisingMember_3352D6FDE2FC01855D4AC8A25CC7F591" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_CFBFB52085A6B8ED9751C8A25CC51571" xlink:to="loc_us-gaap_AdvertisingMember_3352D6FDE2FC01855D4AC8A25CC7F591" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_TheatricalMember" xlink:label="loc_cmcsa_TheatricalMember_2E0DD3DE841DA9387D57C8A25CC71D18" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_CFBFB52085A6B8ED9751C8A25CC51571" xlink:to="loc_cmcsa_TheatricalMember_2E0DD3DE841DA9387D57C8A25CC71D18" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_ContentLicensingAndOtherMember" xlink:label="loc_cmcsa_ContentLicensingAndOtherMember_D6F603DF8692EC7B26BDC8A25CC7C747" xlink:type="locator" />
    <link:definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_CFBFB52085A6B8ED9751C8A25CC51571" xlink:to="loc_cmcsa_ContentLicensingAndOtherMember_D6F603DF8692EC7B26BDC8A25CC7C747" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_ContentLicensingMember" xlink:label="loc_cmcsa_ContentLicensingMember_EE5DEDA8C889125600CEC8A25CC738EA" xlink:type="locator" />
    <link:definitionArc order="12" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_CFBFB52085A6B8ED9751C8A25CC51571" xlink:to="loc_cmcsa_ContentLicensingMember_EE5DEDA8C889125600CEC8A25CC738EA" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_DistributionAndOtherMember" xlink:label="loc_cmcsa_DistributionAndOtherMember_E4A267977EC2000E0C60C8A25CC7986C" xlink:type="locator" />
    <link:definitionArc order="13" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_CFBFB52085A6B8ED9751C8A25CC51571" xlink:to="loc_cmcsa_DistributionAndOtherMember_E4A267977EC2000E0C60C8A25CC7986C" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_HomeEntertainmentMember" xlink:label="loc_cmcsa_HomeEntertainmentMember_21DB6A3296921957BB18C8A25CC85698" xlink:type="locator" />
    <link:definitionArc order="14" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_CFBFB52085A6B8ED9751C8A25CC51571" xlink:to="loc_cmcsa_HomeEntertainmentMember_21DB6A3296921957BB18C8A25CC85698" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_OtherMember" xlink:label="loc_cmcsa_OtherMember_8BE6C13A4533FA3F2C8BC8A25CC801F4" xlink:type="locator" />
    <link:definitionArc order="15" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_CFBFB52085A6B8ED9751C8A25CC51571" xlink:to="loc_cmcsa_OtherMember_8BE6C13A4533FA3F2C8BC8A25CC801F4" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_FranchiseAndOtherRegulatoryFeesMember" xlink:label="loc_cmcsa_FranchiseAndOtherRegulatoryFeesMember_0933FE6F5439242F997FC8A25CC85BD1" xlink:type="locator" />
    <link:definitionArc order="16" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_CFBFB52085A6B8ED9751C8A25CC51571" xlink:to="loc_cmcsa_FranchiseAndOtherRegulatoryFeesMember_0933FE6F5439242F997FC8A25CC85BD1" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_Revenues" xlink:label="loc_us-gaap_Revenues_D94EB39EE36B0F5F1B36C8A25CC8F5B6" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_B58649A6D502285438C8C8A25CC88CD3" xlink:to="loc_us-gaap_Revenues_D94EB39EE36B0F5F1B36C8A25CC8F5B6" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_CableSegmentRevenueTypesAsPercentageOfTotalCableRevenue" xlink:label="loc_cmcsa_CableSegmentRevenueTypesAsPercentageOfTotalCableRevenue_1F0B80FDF6F3F70796FCC8A25CC958CD" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_B58649A6D502285438C8C8A25CC88CD3" xlink:to="loc_cmcsa_CableSegmentRevenueTypesAsPercentageOfTotalCableRevenue_1F0B80FDF6F3F70796FCC8A25CC958CD" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/RevenueRevenueByGeographicLocationDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DisaggregationOfRevenueLineItems" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_02F4D62F21F1ED3B79FCC8A2A084EB04" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DisaggregationOfRevenueTable" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_F8BFB40D144DDC76BD1AC8A2A07D7436" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_02F4D62F21F1ED3B79FCC8A2A084EB04" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_F8BFB40D144DDC76BD1AC8A2A07D7436" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_StatementGeographicalAxis" xlink:label="loc_srt_StatementGeographicalAxis_B54F8AA604405E0F3E95C8A2A07E0C29" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_F8BFB40D144DDC76BD1AC8A2A07D7436" xlink:to="loc_srt_StatementGeographicalAxis_B54F8AA604405E0F3E95C8A2A07E0C29" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_SegmentGeographicalDomain" xlink:label="loc_srt_SegmentGeographicalDomain_B5D7B9B714637DF553C2C8A2A07E7A95_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_B54F8AA604405E0F3E95C8A2A07E0C29" xlink:to="loc_srt_SegmentGeographicalDomain_B5D7B9B714637DF553C2C8A2A07E7A95_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_SegmentGeographicalDomain" xlink:label="loc_srt_SegmentGeographicalDomain_B5D7B9B714637DF553C2C8A2A07E7A95" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_B54F8AA604405E0F3E95C8A2A07E0C29" xlink:to="loc_srt_SegmentGeographicalDomain_B5D7B9B714637DF553C2C8A2A07E7A95" xlink:type="arc" />
    <link:loc xlink:href="https://xbrl.sec.gov/country/2017/country-2017-01-31.xsd#country_US" xlink:label="loc_country_US_40135A432B1B79252B02C8A2A07EC5FA" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_B5D7B9B714637DF553C2C8A2A07E7A95" xlink:to="loc_country_US_40135A432B1B79252B02C8A2A07EC5FA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_EuropeMember" xlink:label="loc_srt_EuropeMember_E04404BA02454964D750C8A2A083E355" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_B5D7B9B714637DF553C2C8A2A07E7A95" xlink:to="loc_srt_EuropeMember_E04404BA02454964D750C8A2A083E355" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_OtherGeographicLocationsMember" xlink:label="loc_cmcsa_OtherGeographicLocationsMember_6D7A163F544CB3BDF3A9C8A2A0840A2F" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_B5D7B9B714637DF553C2C8A2A07E7A95" xlink:to="loc_cmcsa_OtherGeographicLocationsMember_6D7A163F544CB3BDF3A9C8A2A0840A2F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_Revenues" xlink:label="loc_us-gaap_Revenues_5D6DB45D0E9EA240E6A5C8A2A08574D5" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_02F4D62F21F1ED3B79FCC8A2A084EB04" xlink:to="loc_us-gaap_Revenues_5D6DB45D0E9EA240E6A5C8A2A08574D5" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/RevenueTables" xlink:type="extended" />
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/SegmentInformation" xlink:type="extended" />
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/SegmentInformationDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SegmentReportingInformationLineItems" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_F827CD0B82AD7C2F0A16AD5096E38F5D" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_9FC9DC0782763B06E3EBAD5096DFB611" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_F827CD0B82AD7C2F0A16AD5096E38F5D" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_9FC9DC0782763B06E3EBAD5096DFB611" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_ConsolidationItemsAxis" xlink:label="loc_srt_ConsolidationItemsAxis_6B740084816938DD9664AD5096DF9F82" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_9FC9DC0782763B06E3EBAD5096DFB611" xlink:to="loc_srt_ConsolidationItemsAxis_6B740084816938DD9664AD5096DF9F82" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_ConsolidationItemsDomain" xlink:label="loc_srt_ConsolidationItemsDomain_2466C8AB386A4C666A7EAD5096DF02A1_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_6B740084816938DD9664AD5096DF9F82" xlink:to="loc_srt_ConsolidationItemsDomain_2466C8AB386A4C666A7EAD5096DF02A1_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_ConsolidationItemsDomain" xlink:label="loc_srt_ConsolidationItemsDomain_2466C8AB386A4C666A7EAD5096DF02A1" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_6B740084816938DD9664AD5096DF9F82" xlink:to="loc_srt_ConsolidationItemsDomain_2466C8AB386A4C666A7EAD5096DF02A1" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OperatingSegmentsMember" xlink:label="loc_us-gaap_OperatingSegmentsMember_0664DEFD107C7CCE72EFAD5096E0C0B9" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_2466C8AB386A4C666A7EAD5096DF02A1" xlink:to="loc_us-gaap_OperatingSegmentsMember_0664DEFD107C7CCE72EFAD5096E0C0B9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CorporateNonSegmentMember" xlink:label="loc_us-gaap_CorporateNonSegmentMember_50ADD0FA24C753255357AD5096E06A6D" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_2466C8AB386A4C666A7EAD5096DF02A1" xlink:to="loc_us-gaap_CorporateNonSegmentMember_50ADD0FA24C753255357AD5096E06A6D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_MaterialReconcilingItemsMember" xlink:label="loc_us-gaap_MaterialReconcilingItemsMember_D17B9BFE013F3A888F2CAD5096E0CF5C" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_2466C8AB386A4C666A7EAD5096DF02A1" xlink:to="loc_us-gaap_MaterialReconcilingItemsMember_D17B9BFE013F3A888F2CAD5096E0CF5C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementBusinessSegmentsAxis" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_7E1EF451F2F0A7055BABAD5096E1F4DD" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_9FC9DC0782763B06E3EBAD5096DFB611" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_7E1EF451F2F0A7055BABAD5096E1F4DD" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SegmentDomain" xlink:label="loc_us-gaap_SegmentDomain_C4931634E380A468B005AD5096E16758_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_7E1EF451F2F0A7055BABAD5096E1F4DD" xlink:to="loc_us-gaap_SegmentDomain_C4931634E380A468B005AD5096E16758_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SegmentDomain" xlink:label="loc_us-gaap_SegmentDomain_C4931634E380A468B005AD5096E16758" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_7E1EF451F2F0A7055BABAD5096E1F4DD" xlink:to="loc_us-gaap_SegmentDomain_C4931634E380A468B005AD5096E16758" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_CableCommunicationsMember" xlink:label="loc_cmcsa_CableCommunicationsMember_80FECF2C8D5041A236CFAD5096E1A779" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_C4931634E380A468B005AD5096E16758" xlink:to="loc_cmcsa_CableCommunicationsMember_80FECF2C8D5041A236CFAD5096E1A779" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_CableNetworksMember" xlink:label="loc_cmcsa_CableNetworksMember_8ED3D948EC2C74984CE4AD5096E16986" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_C4931634E380A468B005AD5096E16758" xlink:to="loc_cmcsa_CableNetworksMember_8ED3D948EC2C74984CE4AD5096E16986" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_BroadcastTelevisionMember" xlink:label="loc_cmcsa_BroadcastTelevisionMember_A0A1068D3A1A2401696EAD5096E2E825" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_C4931634E380A468B005AD5096E16758" xlink:to="loc_cmcsa_BroadcastTelevisionMember_A0A1068D3A1A2401696EAD5096E2E825" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_FilmedEntertainmentMember" xlink:label="loc_cmcsa_FilmedEntertainmentMember_6F89B84D8F2A0803DF18AD5096E2BA56" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_C4931634E380A468B005AD5096E16758" xlink:to="loc_cmcsa_FilmedEntertainmentMember_6F89B84D8F2A0803DF18AD5096E2BA56" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_ThemeParksMember" xlink:label="loc_cmcsa_ThemeParksMember_41FE2E78E79775910091AD5096E2D5C5" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_C4931634E380A468B005AD5096E16758" xlink:to="loc_cmcsa_ThemeParksMember_41FE2E78E79775910091AD5096E2D5C5" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_NBCUniversalSegmentsMember" xlink:label="loc_cmcsa_NBCUniversalSegmentsMember_3D9D16B535A65E1D3A15AD5096E279AD" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_C4931634E380A468B005AD5096E16758" xlink:to="loc_cmcsa_NBCUniversalSegmentsMember_3D9D16B535A65E1D3A15AD5096E279AD" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_SkyLimitedMember" xlink:label="loc_cmcsa_SkyLimitedMember_F17CF88FE64CA5573A82AD5096E2046F" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_C4931634E380A468B005AD5096E16758" xlink:to="loc_cmcsa_SkyLimitedMember_F17CF88FE64CA5573A82AD5096E2046F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_NumberOfReportableSegments" xlink:label="loc_us-gaap_NumberOfReportableSegments_75B4DC8E3D17E574B072AD5096E3E67A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_F827CD0B82AD7C2F0A16AD5096E38F5D" xlink:to="loc_us-gaap_NumberOfReportableSegments_75B4DC8E3D17E574B072AD5096E3E67A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SegmentReportingInformationProfitLossAbstract" xlink:label="loc_us-gaap_SegmentReportingInformationProfitLossAbstract_0EF4A73AB6BFF9A06693AD5096E33919" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_F827CD0B82AD7C2F0A16AD5096E38F5D" xlink:to="loc_us-gaap_SegmentReportingInformationProfitLossAbstract_0EF4A73AB6BFF9A06693AD5096E33919" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_Revenues" xlink:label="loc_us-gaap_Revenues_22B7B7D47D8BFE68C5CDAD5096E377E7" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationProfitLossAbstract_0EF4A73AB6BFF9A06693AD5096E33919" xlink:to="loc_us-gaap_Revenues_22B7B7D47D8BFE68C5CDAD5096E377E7" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_AdjustedEBITDA" xlink:label="loc_cmcsa_AdjustedEBITDA_9F95EBB4D52FECB4648FAD5096E44C9D" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationProfitLossAbstract_0EF4A73AB6BFF9A06693AD5096E33919" xlink:to="loc_cmcsa_AdjustedEBITDA_9F95EBB4D52FECB4648FAD5096E44C9D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DepreciationAndAmortization" xlink:label="loc_us-gaap_DepreciationAndAmortization_8D9D4D1B68D8CE52A92AAD5096E497BE" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationProfitLossAbstract_0EF4A73AB6BFF9A06693AD5096E33919" xlink:to="loc_us-gaap_DepreciationAndAmortization_8D9D4D1B68D8CE52A92AAD5096E497BE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PaymentsToAcquirePropertyPlantAndEquipment" xlink:label="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_B452F07E6A6B1649B8B8AD5096E4D20C" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationProfitLossAbstract_0EF4A73AB6BFF9A06693AD5096E33919" xlink:to="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_B452F07E6A6B1649B8B8AD5096E4D20C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PaymentsToAcquireIntangibleAssets" xlink:label="loc_us-gaap_PaymentsToAcquireIntangibleAssets_A3C0A323215D73BBAFF5AD5096E59766" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationProfitLossAbstract_0EF4A73AB6BFF9A06693AD5096E33919" xlink:to="loc_us-gaap_PaymentsToAcquireIntangibleAssets_A3C0A323215D73BBAFF5AD5096E59766" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/SegmentInformationReconciliationOfAdjustedEbitdaFromSegmentToConsolidatedStatementsDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/SegmentInformationTables" xlink:type="extended" />
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/SignificantTransactions" xlink:type="extended" />
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/SignificantTransactionsUniversalBeijingResortDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_VariableInterestEntityLineItems" xlink:label="loc_us-gaap_VariableInterestEntityLineItems_C2D41B9480834A9A30DCC1A2C39F27B3" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ScheduleOfVariableInterestEntitiesTable" xlink:label="loc_us-gaap_ScheduleOfVariableInterestEntitiesTable_2C7F5E4449C3922C023EC1A2C39B2C3C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_C2D41B9480834A9A30DCC1A2C39F27B3" xlink:to="loc_us-gaap_ScheduleOfVariableInterestEntitiesTable_2C7F5E4449C3922C023EC1A2C39B2C3C" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_OwnershipAxis" xlink:label="loc_srt_OwnershipAxis_7A5B549E0B8928233B8FC1A2C39C9B7F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfVariableInterestEntitiesTable_2C7F5E4449C3922C023EC1A2C39B2C3C" xlink:to="loc_srt_OwnershipAxis_7A5B549E0B8928233B8FC1A2C39C9B7F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_OwnershipDomain" xlink:label="loc_srt_OwnershipDomain_83CDB9796B372ABB59C8C1A2C39CA982_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_OwnershipAxis_7A5B549E0B8928233B8FC1A2C39C9B7F" xlink:to="loc_srt_OwnershipDomain_83CDB9796B372ABB59C8C1A2C39CA982_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_OwnershipDomain" xlink:label="loc_srt_OwnershipDomain_83CDB9796B372ABB59C8C1A2C39CA982" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_OwnershipAxis_7A5B549E0B8928233B8FC1A2C39C9B7F" xlink:to="loc_srt_OwnershipDomain_83CDB9796B372ABB59C8C1A2C39CA982" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_UniversalBeijingResortMember" xlink:label="loc_cmcsa_UniversalBeijingResortMember_D06CBE61AD92008AE9FDC1A2C39DEB77" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_OwnershipDomain_83CDB9796B372ABB59C8C1A2C39CA982" xlink:to="loc_cmcsa_UniversalBeijingResortMember_D06CBE61AD92008AE9FDC1A2C39DEB77" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_ConsolidatedEntitiesAxis" xlink:label="loc_srt_ConsolidatedEntitiesAxis_A3908F0D764F1BF05D5CC1A2C39DA301" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfVariableInterestEntitiesTable_2C7F5E4449C3922C023EC1A2C39B2C3C" xlink:to="loc_srt_ConsolidatedEntitiesAxis_A3908F0D764F1BF05D5CC1A2C39DA301" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_ConsolidatedEntitiesDomain" xlink:label="loc_srt_ConsolidatedEntitiesDomain_8248C72845DF1EA69F47C1A2C39DBDE8_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_A3908F0D764F1BF05D5CC1A2C39DA301" xlink:to="loc_srt_ConsolidatedEntitiesDomain_8248C72845DF1EA69F47C1A2C39DBDE8_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_ConsolidatedEntitiesDomain" xlink:label="loc_srt_ConsolidatedEntitiesDomain_8248C72845DF1EA69F47C1A2C39DBDE8" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_A3908F0D764F1BF05D5CC1A2C39DA301" xlink:to="loc_srt_ConsolidatedEntitiesDomain_8248C72845DF1EA69F47C1A2C39DBDE8" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_VariableInterestEntityPrimaryBeneficiaryMember" xlink:label="loc_us-gaap_VariableInterestEntityPrimaryBeneficiaryMember_219ED10C612B0C20637AC1A2C39E7A90" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_8248C72845DF1EA69F47C1A2C39DBDE8" xlink:to="loc_us-gaap_VariableInterestEntityPrimaryBeneficiaryMember_219ED10C612B0C20637AC1A2C39E7A90" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DebtInstrumentAxis" xlink:label="loc_us-gaap_DebtInstrumentAxis_F209C8BD9906B25B69A7C1A2C39E47A5" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfVariableInterestEntitiesTable_2C7F5E4449C3922C023EC1A2C39B2C3C" xlink:to="loc_us-gaap_DebtInstrumentAxis_F209C8BD9906B25B69A7C1A2C39E47A5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_DD2EF775080D86291146C1A2C39EBFBB_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_F209C8BD9906B25B69A7C1A2C39E47A5" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_DD2EF775080D86291146C1A2C39EBFBB_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_DD2EF775080D86291146C1A2C39EBFBB" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_F209C8BD9906B25B69A7C1A2C39E47A5" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_DD2EF775080D86291146C1A2C39EBFBB" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_UniversalBeijingResortTermLoansMember" xlink:label="loc_cmcsa_UniversalBeijingResortTermLoansMember_8A7348E5F097A9F7E9B9C1A2C39E7263" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_DD2EF775080D86291146C1A2C39EBFBB" xlink:to="loc_cmcsa_UniversalBeijingResortTermLoansMember_8A7348E5F097A9F7E9B9C1A2C39E7263" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_MinorityInterestOwnershipPercentageByParent" xlink:label="loc_us-gaap_MinorityInterestOwnershipPercentageByParent_23476690A5622AF954FEC1A2C39F38A1" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_C2D41B9480834A9A30DCC1A2C39F27B3" xlink:to="loc_us-gaap_MinorityInterestOwnershipPercentageByParent_23476690A5622AF954FEC1A2C39F38A1" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OtherLongTermDebt" xlink:label="loc_us-gaap_OtherLongTermDebt_03473096A867ABDDFC18C1A2C39FFA6E" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_C2D41B9480834A9A30DCC1A2C39F27B3" xlink:to="loc_us-gaap_OtherLongTermDebt_03473096A867ABDDFC18C1A2C39FFA6E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_Assets" xlink:label="loc_us-gaap_Assets_E783D162B0DDB76A9605C1A2C39FFA5F" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_C2D41B9480834A9A30DCC1A2C39F27B3" xlink:to="loc_us-gaap_Assets_E783D162B0DDB76A9605C1A2C39FFA5F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_Liabilities" xlink:label="loc_us-gaap_Liabilities_E3EE64D7AFC4D21BC678C1A2C39FC0C3" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_C2D41B9480834A9A30DCC1A2C39F27B3" xlink:to="loc_us-gaap_Liabilities_E3EE64D7AFC4D21BC678C1A2C39FC0C3" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/SupplementalFinancialInformation" xlink:type="extended" />
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/SupplementalFinancialInformationCashCashEquivalentsAndRestrictedCashDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/SupplementalFinancialInformationCashPaymentsForInterestAndIncomeTaxesDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/SupplementalFinancialInformationComponentsOfAccumulatedOtherComprehensiveIncomeLossDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/SupplementalFinancialInformationNoncashActivitiesDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/SupplementalFinancialInformationShareBasedCompensationDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_BC5C6D923A03BB683F2AAD5094F5AF37" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_FADB1C22D38764EC321CAD5094F2F836" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_BC5C6D923A03BB683F2AAD5094F5AF37" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_FADB1C22D38764EC321CAD5094F2F836" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PlanNameAxis" xlink:label="loc_us-gaap_PlanNameAxis_5D07255D7AFD4BD449B4AD5094F28217" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_FADB1C22D38764EC321CAD5094F2F836" xlink:to="loc_us-gaap_PlanNameAxis_5D07255D7AFD4BD449B4AD5094F28217" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PlanNameDomain" xlink:label="loc_us-gaap_PlanNameDomain_4B0A3B7E2A8CD9D0B73FAD5094F3030C_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_5D07255D7AFD4BD449B4AD5094F28217" xlink:to="loc_us-gaap_PlanNameDomain_4B0A3B7E2A8CD9D0B73FAD5094F3030C_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PlanNameDomain" xlink:label="loc_us-gaap_PlanNameDomain_4B0A3B7E2A8CD9D0B73FAD5094F3030C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_5D07255D7AFD4BD449B4AD5094F28217" xlink:to="loc_us-gaap_PlanNameDomain_4B0A3B7E2A8CD9D0B73FAD5094F3030C" xlink:type="arc" />
    <link:loc xlink:href="cmcsa-20200331.xsd#cmcsa_ManagementGrantMember" xlink:label="loc_cmcsa_ManagementGrantMember_9EB1D9123CD44F8A3295AD5094F3337C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_4B0A3B7E2A8CD9D0B73FAD5094F3030C" xlink:to="loc_cmcsa_ManagementGrantMember_9EB1D9123CD44F8A3295AD5094F3337C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AwardTypeAxis" xlink:label="loc_us-gaap_AwardTypeAxis_026E64CAB4EBF8912CBAAD5094F393DA" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_FADB1C22D38764EC321CAD5094F2F836" xlink:to="loc_us-gaap_AwardTypeAxis_026E64CAB4EBF8912CBAAD5094F393DA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_0BCC644C264F2A58A1F2AD5094F3EF3E_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_026E64CAB4EBF8912CBAAD5094F393DA" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_0BCC644C264F2A58A1F2AD5094F3EF3E_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_0BCC644C264F2A58A1F2AD5094F3EF3E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_026E64CAB4EBF8912CBAAD5094F393DA" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_0BCC644C264F2A58A1F2AD5094F3EF3E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_RestrictedStockUnitsRSUMember" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_3B54D0A619CA49BE90C5AD5094F48710" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_0BCC644C264F2A58A1F2AD5094F3EF3E" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_3B54D0A619CA49BE90C5AD5094F48710" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_EmployeeStockOptionMember" xlink:label="loc_us-gaap_EmployeeStockOptionMember_4BBD38F88B05B17494F5AD5094F4F515" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_0BCC644C264F2A58A1F2AD5094F3EF3E" xlink:to="loc_us-gaap_EmployeeStockOptionMember_4BBD38F88B05B17494F5AD5094F4F515" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_EmployeeStockMember" xlink:label="loc_us-gaap_EmployeeStockMember_D40FFA970C1C82F5C41AAD5094F4203F" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_0BCC644C264F2A58A1F2AD5094F3EF3E" xlink:to="loc_us-gaap_EmployeeStockMember_D40FFA970C1C82F5C41AAD5094F4203F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_9A448C8F80906F8B9A67AD5094F54759" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_BC5C6D923A03BB683F2AAD5094F5AF37" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_9A448C8F80906F8B9A67AD5094F54759" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_F66579D383857178F69DAD5094F6671F" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_BC5C6D923A03BB683F2AAD5094F5AF37" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_F66579D383857178F69DAD5094F6671F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_EB3D575CA93D0734F959AD5094F68EBE" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_BC5C6D923A03BB683F2AAD5094F5AF37" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_EB3D575CA93D0734F959AD5094F68EBE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_0F56DFEF59856D46B1E0AD5094F6B46F" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_BC5C6D923A03BB683F2AAD5094F5AF37" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_0F56DFEF59856D46B1E0AD5094F6B46F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AllocatedShareBasedCompensationExpense" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_5A070F480480AD3E3866AD5094F6DC0A" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_BC5C6D923A03BB683F2AAD5094F5AF37" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_5A070F480480AD3E3866AD5094F6DC0A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_75FBC2EF59F096147769AD5094F72AB4" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_BC5C6D923A03BB683F2AAD5094F5AF37" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_75FBC2EF59F096147769AD5094F72AB4" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://corporate.comcast.com/role/SupplementalFinancialInformationTables" xlink:type="extended" />
</link:linkbase>
