<SUBMISSION>
<ACCESSION-NUMBER>0001179110-03-012602
<TYPE>4
<PUBLIC-DOCUMENT-COUNT>1
<PERIOD>20031212
<FILING-DATE>20031215
<REPORTING-OWNER>
<OWNER-DATA>
<CONFORMED-NAME>CASSIN BJ
<CIK>0001193205
</OWNER-DATA>
<FILING-VALUES>
<FORM-TYPE>4
<ACT>34
<FILE-NUMBER>000-21937
<FILM-NUMBER>031055507
</FILING-VALUES>
<MAIL-ADDRESS>
<STREET1>C/O CERUS CORP
<STREET2>2411 STENWELL DRIVE
<CITY>CONCORD
<STATE>CA
<ZIP>94520
</MAIL-ADDRESS>
</REPORTING-OWNER>
<ISSUER>
<COMPANY-DATA>
<CONFORMED-NAME>CERUS CORP
<CIK>0001020214
<ASSIGNED-SIC>2836
<IRS-NUMBER>680262011
<STATE-OF-INCORPORATION>DE
<FISCAL-YEAR-END>1231
</COMPANY-DATA>
<BUSINESS-ADDRESS>
<STREET1>2411 STANWELL DR
<CITY>CONCORD
<STATE>CA
<ZIP>94520
<PHONE>9252886000
</BUSINESS-ADDRESS>
<MAIL-ADDRESS>
<STREET1>2525 STANWELL DRIVE
<STREET2>STE 300
<CITY>CONCORD
<STATE>CA
<ZIP>94520
</MAIL-ADDRESS>
<FORMER-COMPANY>
<FORMER-CONFORMED-NAME>CERUS TECHNOLOGIES INC
<DATE-CHANGED>19960731
</FORMER-COMPANY>
</ISSUER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>edgar.xml
<DESCRIPTION>FORM 4 -
<TEXT>
<XML>
<ownershipDocument>
    <schemaVersion>X0201</schemaVersion>

    <documentType>4</documentType>
<periodOfReport>2003-12-12</periodOfReport>
<notSubjectToSection16>0</notSubjectToSection16>
    <issuer>
        <issuerCik>0001020214</issuerCik>
        <issuerName>CERUS CORP</issuerName>
        <issuerTradingSymbol>CERS</issuerTradingSymbol>
</issuer>
<reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001193205</rptOwnerCik>
            <rptOwnerName>CASSIN BJ</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>3000 SAND HILL ROAD</rptOwnerStreet1>
            <rptOwnerStreet2>BUILDING 3, SUITE 210</rptOwnerStreet2>
            <rptOwnerCity>MENLO PARK</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>94025</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
            <reportingOwnerRelationship>
<isDirector>1</isDirector>
<isOfficer>0</isOfficer>
<isTenPercentOwner>0</isTenPercentOwner>
<isOther>0</isOther>
<officerTitle></officerTitle>
<otherText></otherText>
</reportingOwnerRelationship>
</reportingOwner>
<nonDerivativeTable><nonDerivativeTransaction><securityTitle><value>Common Stock</value>
</securityTitle>
<transactionDate><value>2003-12-12</value>
</transactionDate>
<deemedExecutionDate><value>2003-12-12</value>
</deemedExecutionDate>
<transactionCoding><transactionFormType>4</transactionFormType>
<transactionCode>S</transactionCode>
<equitySwapInvolved>0</equitySwapInvolved>
</transactionCoding>
<transactionAmounts><transactionShares><value>9463</value>
</transactionShares>
<transactionPricePerShare><value>4.00</value>
</transactionPricePerShare>
<transactionAcquiredDisposedCode><value>D</value>
</transactionAcquiredDisposedCode>
</transactionAmounts>
<postTransactionAmounts><sharesOwnedFollowingTransaction><value>0</value>
</sharesOwnedFollowingTransaction>
</postTransactionAmounts>
<ownershipNature><directOrIndirectOwnership><value>I</value>
</directOrIndirectOwnership>
<natureOfOwnership><value>By Partnership</value>
<footnoteId id="F1"></footnoteId>
</natureOfOwnership>
</ownershipNature>
</nonDerivativeTransaction>
<nonDerivativeHolding><securityTitle><value>Common Stock</value>
</securityTitle>
<postTransactionAmounts><sharesOwnedFollowingTransaction><value>85000</value>
</sharesOwnedFollowingTransaction>
</postTransactionAmounts>
<ownershipNature><directOrIndirectOwnership><value>I</value>
</directOrIndirectOwnership>
<natureOfOwnership><value>By Foundation</value>
<footnoteId id="F2"></footnoteId>
</natureOfOwnership>
</ownershipNature>
</nonDerivativeHolding>
<nonDerivativeHolding><securityTitle><value>Common Stock</value>
</securityTitle>
<postTransactionAmounts><sharesOwnedFollowingTransaction><value>382684</value>
</sharesOwnedFollowingTransaction>
</postTransactionAmounts>
<ownershipNature><directOrIndirectOwnership><value>I</value>
</directOrIndirectOwnership>
<natureOfOwnership><value>By Trust</value>
<footnoteId id="F3"></footnoteId>
</natureOfOwnership>
</ownershipNature>
</nonDerivativeHolding>
<nonDerivativeHolding><securityTitle><value>Common Stock</value>
</securityTitle>
<postTransactionAmounts><sharesOwnedFollowingTransaction><value>69841</value>
</sharesOwnedFollowingTransaction>
</postTransactionAmounts>
<ownershipNature><directOrIndirectOwnership><value>I</value>
</directOrIndirectOwnership>
<natureOfOwnership><value>By Partnership</value>
<footnoteId id="F4"></footnoteId>
</natureOfOwnership>
</ownershipNature>
</nonDerivativeHolding>
</nonDerivativeTable>
<derivativeTable></derivativeTable>
<footnotes><footnote id="F1">These securities are owned directly by Coral Group Inc. Escrow Agent FBO Partner Brendan Joseph Cassin and Isabel B. Cassin, Tr., UA 01/31/96, Cassin Family Trust.  The Reporting Person is a Trustee of such entity and disclaims beneficial ownership of these securities except to the extent of his pecuniary interest therein.</footnote>
<footnote id="F2">These securities are beneficially owned directly by Cassin Educational Foundation.  The Reporting Person is the Chairman/President of such entity and disclaims beneficial ownership of these securities except to the extent of his pecuniary interest therein.</footnote>
<footnote id="F3">These securities are beneficially owned directly by Brendan Joseph Cassin and Isabel B. Cassin, Tr., UA 01/31/96, Cassin Family Trust.  The Reporting Person is a Trustee of such entity and disclaims beneficial ownership of these securities except to the extent of his pecuniary interest therein.</footnote>
<footnote id="F4">These securities are beneficially owned directly by Cassin Family Partnership.  The Reporting Person is a General Partner of such entity and disclaims beneficial ownership of these securities except to the extent of his proportionate partnership interest therein.</footnote>
</footnotes>
<ownerSignature><signatureName>B. J. Cassin</signatureName>
<signatureDate>2003-12-12</signatureDate>
</ownerSignature>
</ownershipDocument>

</XML>
</TEXT>
</DOCUMENT>
</SUBMISSION>
