<SUBMISSION>
<ACCESSION-NUMBER>0001191727-03-000016
<TYPE>4
<PUBLIC-DOCUMENT-COUNT>1
<PERIOD>20030611
<FILING-DATE>20030612
<REPORTING-OWNER>
<OWNER-DATA>
<CONFORMED-NAME>ROMEO CARMEN
<CIK>0001191727
</OWNER-DATA>
<FILING-VALUES>
<FORM-TYPE>4
<ACT>34
<FILE-NUMBER>000-10200
<FILM-NUMBER>03741564
</FILING-VALUES>
<BUSINESS-ADDRESS>
<STREET1>SEI INVESTMENT INC
<STREET2>ONE FREEDOM VALLEY
<CITY>OAKS
<STATE>PA
<ZIP>19456
</BUSINESS-ADDRESS>
</REPORTING-OWNER>
<ISSUER>
<COMPANY-DATA>
<CONFORMED-NAME>SEI CORP
<CIK>0000350894
<ASSIGNED-SIC>6211
<IRS-NUMBER>231707341
<STATE-OF-INCORPORATION>PA
<FISCAL-YEAR-END>1231
</COMPANY-DATA>
<BUSINESS-ADDRESS>
<STREET1>1 FREEDOM VALLEY DRIVE
<CITY>OAKS
<STATE>PA
<ZIP>19456-1100
<PHONE>6106761000
</BUSINESS-ADDRESS>
<MAIL-ADDRESS>
<STREET1>1 FREEDOM VALLEY DRIVE
<CITY>OAKS
<STATE>PA
<ZIP>19456-1100
</MAIL-ADDRESS>
</ISSUER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>edgar.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>
    <schemaVersion>X0101</schemaVersion>

    <documentType>4</documentType><periodOfReport>2003-06-11</periodOfReport>
    <issuer>
        <issuerCik>0000350894</issuerCik>
        <issuerName>SEI CORP</issuerName>
        <issuerTradingSymbol>SEIC</issuerTradingSymbol></issuer><reportingOwner><reportingOwnerId>
            <rptOwnerCik>0001191727</rptOwnerCik>
            <rptOwnerName>ROMEO CARMEN</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>  </rptOwnerStreet1>
            <rptOwnerStreet2>  </rptOwnerStreet2>
            <rptOwnerCity>  </rptOwnerCity>
            <rptOwnerState>  </rptOwnerState>
            <rptOwnerZipCode>  </rptOwnerZipCode>
        </reportingOwnerAddress>
            <reportingOwnerRelationship>
<isDirector>1</isDirector><isOfficer>1</isOfficer><isTenPercentOwner>0</isTenPercentOwner><isOther>0</isOther><officerTitle>Executive Vice President</officerTitle></reportingOwnerRelationship></reportingOwner><nonDerivativeSecurity><securityTitle><value>Common Stock</value></securityTitle><transactionDate><value>2003-06-11</value></transactionDate><transactionCoding><transactionFormType>4</transactionFormType><transactionCode>S</transactionCode><equitySwapInvolved>0</equitySwapInvolved></transactionCoding><transactionAmounts><transactionShares><value>5000</value></transactionShares><transactionValue><value>30.80</value></transactionValue><transactionAcquiredDisposedCode><value>D</value></transactionAcquiredDisposedCode></transactionAmounts><postTransactionAmounts><sharesOwnedFollowingTransaction><value>1801580</value><footnoteId id="F1"/></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>D</value></directOrIndirectOwnership><natureOfOwnership><value></value></natureOfOwnership></ownershipNature></nonDerivativeSecurity><nonDerivativeSecurity><securityTitle><value>Common Stock</value></securityTitle><transactionDate><value>2003-06-11</value></transactionDate><transactionCoding><transactionFormType>4</transactionFormType><transactionCode>S</transactionCode><equitySwapInvolved>0</equitySwapInvolved></transactionCoding><transactionAmounts><transactionShares><value>5000</value></transactionShares><transactionValue><value>31.00</value></transactionValue><transactionAcquiredDisposedCode><value>D</value></transactionAcquiredDisposedCode></transactionAmounts><postTransactionAmounts><sharesOwnedFollowingTransaction><value>1796580</value><footnoteId id="F1"/></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>D</value></directOrIndirectOwnership><natureOfOwnership><value></value></natureOfOwnership></ownershipNature></nonDerivativeSecurity><nonDerivativeSecurity><securityTitle><value>Common Stock</value></securityTitle><transactionDate><value>2003-06-11</value></transactionDate><transactionCoding><transactionFormType>4</transactionFormType><transactionCode>S</transactionCode><equitySwapInvolved>0</equitySwapInvolved></transactionCoding><transactionAmounts><transactionShares><value>5000</value></transactionShares><transactionValue><value>31.15</value></transactionValue><transactionAcquiredDisposedCode><value>D</value></transactionAcquiredDisposedCode></transactionAmounts><postTransactionAmounts><sharesOwnedFollowingTransaction><value>1791580</value><footnoteId id="F1"/></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>D</value></directOrIndirectOwnership><natureOfOwnership><value></value></natureOfOwnership></ownershipNature></nonDerivativeSecurity><nonDerivativeSecurity><securityTitle><value>Common Stock</value></securityTitle><transactionDate><value>2003-06-11</value></transactionDate><transactionCoding><transactionFormType>4</transactionFormType><transactionCode>S</transactionCode><equitySwapInvolved>0</equitySwapInvolved></transactionCoding><transactionAmounts><transactionShares><value>3000</value></transactionShares><transactionValue><value>31.20</value></transactionValue><transactionAcquiredDisposedCode><value>D</value></transactionAcquiredDisposedCode></transactionAmounts><postTransactionAmounts><sharesOwnedFollowingTransaction><value>1788580</value><footnoteId id="F1"/></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>D</value></directOrIndirectOwnership><natureOfOwnership><value></value></natureOfOwnership></ownershipNature></nonDerivativeSecurity><footnotes><footnote id="F1">This reported number does not include indirectly held shares -  35,000 shares held by his wife, 35,800 shares held in custodianship for the benefit of the reporting person's minor children and 29,296.19 shares of common stock held through the Issuer's 401(K) Plan, based upon a December 31, 2002 plan statement. The reporting person disclaims benefical ownership of all securities held in custodianship for the beneift of his minor children and this report should not be deemed as an adminssion that the reporting persons is the beneficial ownser of such securities for purposes of Section 16 or for any other purpose.</footnote></footnotes><ownerSignature><signatureName>Michelle Vaughn (Attorney-in-Fact)</signatureName><signatureDate>2003-06-12</signatureDate></ownerSignature></ownershipDocument>

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