<SUBMISSION>
<ACCESSION-NUMBER>0000350894-04-000045
<TYPE>3/A
<PUBLIC-DOCUMENT-COUNT>1
<PERIOD>20010529
<FILING-DATE>20040318
<REPORTING-OWNER>
<OWNER-DATA>
<CONFORMED-NAME>BLUMENSTEIN SARAH
<CIK>0001191716
</OWNER-DATA>
<FILING-VALUES>
<FORM-TYPE>3/A
<ACT>34
<FILE-NUMBER>000-10200
<FILM-NUMBER>04676851
</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>3/A
<SEQUENCE>1
<FILENAME>edgar.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0201</schemaVersion>

    <documentType>3/A</documentType>

    <periodOfReport>2001-05-29</periodOfReport>

    <dateOfOriginalSubmission>2001-06-12</dateOfOriginalSubmission>

    <noSecuritiesOwned>0</noSecuritiesOwned>

    <issuer>
        <issuerCik>0000350894</issuerCik>
        <issuerName>SEI CORP</issuerName>
        <issuerTradingSymbol>SEIC</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001191716</rptOwnerCik>
            <rptOwnerName>BLUMENSTEIN SARAH</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>ONE FREEDOM VALLEY DRIVE</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>OAKS</rptOwnerCity>
            <rptOwnerState>PA</rptOwnerState>
            <rptOwnerZipCode>19456</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>1744</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeHolding>
            <securityTitle>
                <value>Stock Option ( Right to Buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>41.45</value>
            </conversionOrExercisePrice>
            <exerciseDate>
                <value>2008-05-29</value>
                <footnoteId id="F1"/>
            </exerciseDate>
            <expirationDate>
                <value>2011-05-29</value>
                <footnoteId id="F2"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>8000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeHolding>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">&quot;Date Exercisable&quot; represents seven years from the date of the grant.  The options vests upon the earlier of SEI's attainment of specific levels of earnings per share or seven years from the date of the grant.</footnote>
        <footnote id="F2">The option expires on the ten year anniversary of the date of the grant.</footnote>
    </footnotes>

    <remarks>This form amends and supercedes the original Form 3, filed on behalf of Ms. Blumenstein on June 12, 2001, to reflect the grant of 8,000 stock options to Ms. Blumenstein upon becoming a director of SEI Investments Company.</remarks>

    <ownerSignature>
        <signatureName>Michelle Vaughn (attorney-in-fact)</signatureName>
        <signatureDate>2004-03-18</signatureDate>
    </ownerSignature>
</ownershipDocument>

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