<SUBMISSION>
<ACCESSION-NUMBER>0001181431-04-027845
<TYPE>3
<PUBLIC-DOCUMENT-COUNT>1
<PERIOD>20040525
<FILING-DATE>20040526
<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>
<REPORTING-OWNER>
<OWNER-DATA>
<CONFORMED-NAME>SMITH THOMAS W
<CIK>0000926688
</OWNER-DATA>
<FILING-VALUES>
<FORM-TYPE>3
<ACT>34
<FILE-NUMBER>000-10200
<FILM-NUMBER>04831999
</FILING-VALUES>
<BUSINESS-ADDRESS>
<STREET1>323 RAILROAD AVENUE
<CITY>GREENWICH
<STATE>CT
<ZIP>06830
<PHONE>2036611200
</BUSINESS-ADDRESS>
<MAIL-ADDRESS>
<STREET1>323 RAILROAD AVENUE
<CITY>GREENWICH
<STATE>CT
<ZIP>06830
</MAIL-ADDRESS>
<FORMER-NAME>
<FORMER-CONFORMED-NAME>THOMAS W SMITH
<DATE-CHANGED>19940713
</FORMER-NAME>
</REPORTING-OWNER>
<DOCUMENT>
<TYPE>3
<SEQUENCE>1
<FILENAME>rrd43666.xml
<DESCRIPTION>INITIAL FORM 3 UPON MR. SMITH'S ELECTION AS DIRECTOR OF SEIC
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>3</documentType>

    <periodOfReport>2004-05-25</periodOfReport>

    <noSecuritiesOwned>0</noSecuritiesOwned>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0000926688</rptOwnerCik>
            <rptOwnerName>SMITH THOMAS W</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>323 RAILROAD AVENUE</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>GREENWICH</rptOwnerCity>
            <rptOwnerState>CT</rptOwnerState>
            <rptOwnerZipCode>06830</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>1100000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>298100</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By Smith Family Accounts</value>
                    <footnoteId id="F1"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>20000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By Prescott Capital Partners LP</value>
                    <footnoteId id="F2"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>2784114</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By Idoya Partners LP</value>
                    <footnoteId id="F3"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>2408805</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By Prescott Associates</value>
                    <footnoteId id="F4"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>163900</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By Prescott International Partners</value>
                    <footnoteId id="F5"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>234100</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By Prescott International Partners Profit Sharing Trust</value>
                    <footnoteId id="F6"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>65000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By the Thomas W. Smith Foundation</value>
                    <footnoteId id="F7"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>40000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By Petra Capital Partners</value>
                    <footnoteId id="F8"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">These shares are owned directly by accounts established for the benefit of certain family members of the Reporting Person.  The inclusion of these shares in this report shall not be deemed an admission of beneficial ownership for purposes of Section 16 or any other purpose and the Reporting Person disclaims beneficial ownership of these shares except to the extent of his pecuniary interest therein</footnote>
        <footnote id="F2">These shares are owned directly by Prescott Capital Partners LP (&quot;PCP&quot;), a private investment limited partnership, and indirectly by the Reporting Person as a general partner of PCP. The Reporting Person disclaims beneficial ownership of these shares in excess of his interest under 16a-1(a)(2)(ii)(B). The address for PCP is 323 Railroad Avenue, Greenwich, CT 06830</footnote>
        <footnote id="F3">These shares are owned directly by Idoya Partners (&quot;Idoya&quot;),  a private investment limited partnership, and indirectly by the Reporting Person as a general partner of Idoya. The Reporting Person disclaims beneficial ownership of these shares in excess of his interest under 16a-1(a)(2)(ii)(B). The address for Idoya is 323 Railroad Avenue, Greenwich, CT 06830</footnote>
        <footnote id="F4">These shares are owned directly by Prescott Associates, a private investment limited partnership, and indirectly by the Reporting Person as a general partner of Prescott Associates. The Reporting Person disclaims beneficial ownership of these shares in excess of his interest under 16a-1(a)(2)(ii)(B). The address for Prescott Associates is 323 Railroad Avenue, Greenwich, CT 06830</footnote>
        <footnote id="F5">These shares are owned directly by Prescott International Partners (&quot;PIP&quot;), a private investment limited partnership, and indirectly by the Reporting Person as a general partner of PIP. The Reporting Person disclaims beneficial ownership of these shares in excess of his interest under 16a-1(a)(2)(ii)(B). The address for PIP is 323 Railroad Avenue, Greenwich, CT 06830</footnote>
        <footnote id="F6">These shares are owned directly by the Prescott International Partners Profit Sharing Trust (the &quot;Trust&quot;) and indirectly by the Reporting Person as trustee of the Trust. The Reporting Person disclaims beneficial ownership of these shares in excess of his interest under 16a-8(b)(2)(ii). The address for the Trust is 323 Railroad Avenue, Greenwich, CT 06830</footnote>
        <footnote id="F7">These shares are owned directly by the Thomas W. Smith Foundation (&quot;Foundation&quot;), a private charitable foundation,  and indirectly by the Reporting Person as trustee of the Foundation. The Reporting Person disclaims beneficial ownership of these shares in excess of his interest under 16a-8(b)(2)(ii). The address for the Foundation is 323 Railroad Avenue, Greenwich, CT 06830</footnote>
        <footnote id="F8">These shares are owned directly by Petra Capital Partners (&quot;Petra&quot;), a private investment limited partnership, and indirectly by the Reporting Person as a general partner of Petra. The Reporting Person disclaims beneficial ownership of these shares in excess of his interest under 16a-1(a)(2)(ii)(B). The address for Petra is 323 Railroad Avenue, Greenwich, CT 06830</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Thomas W. Smith</signatureName>
        <signatureDate>2004-05-26</signatureDate>
    </ownerSignature>
</ownershipDocument>

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