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Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
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MIC-Info: RSA-MD5,RSA,
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<SEC-DOCUMENT>0001131399-10-000001.txt : 20100104
<SEC-HEADER>0001131399-10-000001.hdr.sgml : 20100101
<ACCEPTANCE-DATETIME>20100104135027
ACCESSION NUMBER:		0001131399-10-000001
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20091230
FILED AS OF DATE:		20100104
DATE AS OF CHANGE:		20100104

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			MAXYGEN INC
		CENTRAL INDEX KEY:			0001068796
		STANDARD INDUSTRIAL CLASSIFICATION:	SERVICES-COMMERCIAL PHYSICAL & BIOLOGICAL RESEARCH [8731]
		IRS NUMBER:				770449487
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		515 GALVESTON DRIVE
		CITY:			REDWOOD CITY
		STATE:			CA
		ZIP:			94063
		BUSINESS PHONE:		6502985300

	MAIL ADDRESS:	
		STREET 1:		515 GALVESTON DRIVE
		CITY:			REDWOOD CITY
		STATE:			CA
		ZIP:			94063

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			GLAXOSMITHKLINE PLC
		CENTRAL INDEX KEY:			0001131399
		STANDARD INDUSTRIAL CLASSIFICATION:	PHARMACEUTICAL PREPARATIONS [2834]

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-28401
		FILM NUMBER:		10501282

	BUSINESS ADDRESS:	
		STREET 1:		980 GREAT WEST ROAD
		CITY:			BRENTFORD MIDDLESEX
		STATE:			X0
		ZIP:			TW8 9GS
		BUSINESS PHONE:		011442080475000

	MAIL ADDRESS:	
		STREET 1:		980 GREAT WEST ROAD
		CITY:			BRENTFORD MIDDLESEX
		STATE:			X0
		ZIP:			TW8 9GS
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>primary_doc.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2009-12-30</periodOfReport>

    <notSubjectToSection16>1</notSubjectToSection16>

    <issuer>
        <issuerCik>0001068796</issuerCik>
        <issuerName>MAXYGEN INC</issuerName>
        <issuerTradingSymbol>MAXY</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001131399</rptOwnerCik>
            <rptOwnerName>GLAXOSMITHKLINE PLC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>980 GREAT WEST ROAD</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>BRENTFORD MIDDLESEX</rptOwnerCity>
            <rptOwnerState>X0</rptOwnerState>
            <rptOwnerZipCode>TW8 9GS</rptOwnerZipCode>
            <rptOwnerStateDescription>UNITED KINGDOM</rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock par value $0.0001 per share</value>
            </securityTitle>
            <transactionDate>
                <value>2009-12-30</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>5121488</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>5.3</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>1433361</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By Corporation</value>
                    <footnoteId id="F1"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">All shares covered by this report are beneficially owned by direct or indirect wholly-owned subsidiaries of Reporting Person. The Reporting Person may be deemed, for the purposes of Section 16 of the Securities Exchange Act of 1934, as amended (the &quot;Act&quot;) to be the beneficial owner of Glaxo Group Limited and GlaxoSmithKline Services Unlimited and, therefore, may be deemed to be a &quot;10 per cent beneficial owner&quot; for the purposes of Section 16 of the Act.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Victoria Whyte, Deputy Company Secretary</signatureName>
        <signatureDate>2009-01-04</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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