<?xml version="1.0"?>
<ownershipDocument>
    <schemaVersion>X0101</schemaVersion>

    <documentType>4</documentType>
	<periodOfReport>2003-07-23</periodOfReport>
	<notSubjectToSection16>0</notSubjectToSection16>
    <issuer>
        <issuerCik>0000732485</issuerCik>
        <issuerName>GENZYME CORP</issuerName>
        <issuerTradingSymbol>GENZ</issuerTradingSymbol>
	</issuer>
	<reportingOwner>
		<reportingOwnerId>
            <rptOwnerCik>0001021041</rptOwnerCik>
            <rptOwnerName>WIRTH PETER</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>  </rptOwnerStreet1>
            <rptOwnerStreet2>  </rptOwnerStreet2>
            <rptOwnerCity>  </rptOwnerCity>
            <rptOwnerState>  </rptOwnerState>
            <rptOwnerZipCode>  </rptOwnerZipCode>
        </reportingOwnerAddress>
            <reportingOwnerRelationship>
			<isDirector>0</isDirector>
			<isOfficer>1</isOfficer>
			<isTenPercentOwner>0</isTenPercentOwner>
			<isOther>0</isOther>
			<officerTitle>Executive Vice President</officerTitle>
		</reportingOwnerRelationship>
	</reportingOwner>
	<nonDerivativeSecurity>
		<securityTitle>
			<value>Genzyme General common stock (GENZ)</value>
		</securityTitle>
		<transactionDate>
			<value>2003-07-23</value>
		</transactionDate>
		<deemedExecutionDate>
			<value>2003-07-23</value>
		</deemedExecutionDate>
		<transactionCoding>
			<transactionFormType>4</transactionFormType>
			<transactionCode>S</transactionCode>
			<equitySwapInvolved>0</equitySwapInvolved>
			<footnoteId id="F1"/>
		</transactionCoding>
		<transactionAmounts>
			<transactionShares>
				<value>34320</value>
			</transactionShares>
			<transactionValue>
				<value>50.01</value>
			</transactionValue>
			<transactionAcquiredDisposedCode>
				<value>D</value>
			</transactionAcquiredDisposedCode>
		</transactionAmounts>
		<postTransactionAmounts>
			<sharesOwnedFollowingTransaction>
				<value>7761</value>
				<footnoteId id="F2"/>
			</sharesOwnedFollowingTransaction>
		</postTransactionAmounts>
		<ownershipNature>
			<directOrIndirectOwnership>
				<value>D</value>
			</directOrIndirectOwnership>
			<natureOfOwnership>
				<value/>
			</natureOfOwnership>
		</ownershipNature>
	</nonDerivativeSecurity>
	<footnotes>
		<footnote id="F1">The sales reported were effected pursuant to a Rule 10b5-1 trading plan adpoted by the reporting person on June 16, 2003.</footnote>
		<footnote id="F2">Includes 421 shares purchased from the issuer's Employee Stock Purchase Plan on July 9, 2003.</footnote>
	</footnotes>
	<ownerSignature>
		<signatureName>By: Susan P. Cogswell, Attorney-in-Fact</signatureName>
		<signatureDate>2003-07-23</signatureDate>
	</ownerSignature>
</ownershipDocument>
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X0101
4
2003-07-23
0
0000732485
GENZYME CORP
GENZ
0001021041
WIRTH PETER
0
1
0
0
Executive Vice President
Genzyme General common stock (GENZ)
2003-07-23
2003-07-23
4
S
0
34320
50.01
D
7761
D
The sales reported were effected pursuant to a Rule 10b5-1 trading plan adpoted by the reporting person on June 16, 2003.
Includes 421 shares purchased from the issuer's Employee Stock Purchase Plan on July 9, 2003.
By: Susan P. Cogswell, Attorney-in-Fact
2003-07-23