<?xml version="1.0" encoding="UTF-8"?>
<edgarSubmission xmlns="http://www.sec.gov/edgar/thirteenffiler" xmlns:com="http://www.sec.gov/edgar/common">
  <schemaVersion>X0202</schemaVersion>
  <headerData>
    <submissionType>13F-HR</submissionType>
    <filerInfo>
      <liveTestFlag>LIVE</liveTestFlag>
      <flags>
        <confirmingCopyFlag>false</confirmingCopyFlag>
        <returnCopyFlag>false</returnCopyFlag>
        <overrideInternetFlag>false</overrideInternetFlag>
      </flags>
      <filer>
        <credentials>
          <cik>0000350894</cik>
          <ccc>XXXXXXXX</ccc>
        </credentials>
      </filer>
      <periodOfReport>09-30-2025</periodOfReport>
    </filerInfo>
  </headerData>
  <formData>
    <coverPage>
      <reportCalendarOrQuarter>09-30-2025</reportCalendarOrQuarter>
      <filingManager>
        <name>SEI INVESTMENTS CO</name>
        <address>
          <com:street1>1 FREEDOM VALLEY DRIVE</com:street1>
          <com:city>OAKS</com:city>
          <com:stateOrCountry>PA</com:stateOrCountry>
          <com:zipCode>19456-1100</com:zipCode>
        </address>
      </filingManager>
      <reportType>13F COMBINATION REPORT</reportType>
      <form13FFileNumber>028-16454</form13FFileNumber>
      <otherManagersInfo>
        <otherManager>
          <cik>0000916542</cik>
          <form13FFileNumber>028-05990</form13FFileNumber>
          <name>ACADIAN ASSET MANAGEMENT LLC</name>
        </otherManager>
        <otherManager>
          <cik>0001109448</cik>
          <form13FFileNumber>028-10562</form13FFileNumber>
          <name>ALLIANCEBERNSTEIN L.P.</name>
        </otherManager>
        <otherManager>
          <cik>0001167557</cik>
          <form13FFileNumber>028-10120</form13FFileNumber>
          <name>AQR CAPITAL MANAGEMENT LLC</name>
        </otherManager>
        <otherManager>
          <cik>0001651960</cik>
          <form13FFileNumber>028-17137</form13FFileNumber>
          <name>Arcus Capital Partners, LLC</name>
        </otherManager>
        <otherManager>
          <cik>0001483859</cik>
          <form13FFileNumber>028-13791</form13FFileNumber>
          <name>ArrowMark Colorado Holdings LLC</name>
        </otherManager>
        <otherManager>
          <cik>0001109147</cik>
          <form13FFileNumber>028-05615</form13FFileNumber>
          <name>AXIOM INVESTORS LLC /DE</name>
        </otherManager>
        <otherManager>
          <cik>0001361974</cik>
          <form13FFileNumber>028-11939</form13FFileNumber>
          <name>Beutel, Goodman &amp; Co Ltd.</name>
        </otherManager>
        <otherManager>
          <cik>0001421306</cik>
          <form13FFileNumber>028-12820</form13FFileNumber>
          <name>BRIGADE CAPITAL MANAGEMENT, LP</name>
        </otherManager>
        <otherManager>
          <cik>0001165797</cik>
          <form13FFileNumber>028-11728</form13FFileNumber>
          <name>CAUSEWAY CAPITAL MANAGEMENT LLC</name>
        </otherManager>
        <otherManager>
          <cik>0001350585</cik>
          <form13FFileNumber>028-11563</form13FFileNumber>
          <name>Coho Partners, Ltd.</name>
        </otherManager>
        <otherManager>
          <cik>0001541743</cik>
          <form13FFileNumber>028-14668</form13FFileNumber>
          <name>Copeland Capital Management, LLC</name>
        </otherManager>
        <otherManager>
          <cik>0001505817</cik>
          <form13FFileNumber>028-14036</form13FFileNumber>
          <name>Fiera Capital Corp</name>
        </otherManager>
        <otherManager>
          <cik>0001078013</cik>
          <form13FFileNumber>028-05229</form13FFileNumber>
          <name>GREAT LAKES ADVISORS, LLC</name>
        </otherManager>
        <otherManager>
          <cik>0001368465</cik>
          <form13FFileNumber>028-11957</form13FFileNumber>
          <name>Hillsdale Investment Management Inc.</name>
        </otherManager>
        <otherManager>
          <cik>0001086318</cik>
          <form13FFileNumber>028-04211</form13FFileNumber>
          <name>INTECH INVESTMENT MANAGEMENT LLC</name>
        </otherManager>
        <otherManager>
          <cik>0000940755</cik>
          <form13FFileNumber>028-14777</form13FFileNumber>
          <name>J O HAMBRO CAPITAL MANAGEMENT LTD</name>
        </otherManager>
        <otherManager>
          <cik>0001387369</cik>
          <form13FFileNumber>028-17689</form13FFileNumber>
          <name>KETTLE HILL CAPITAL MANAGEMENT, LLC</name>
        </otherManager>
        <otherManager>
          <cik>0001470944</cik>
          <form13FFileNumber>028-13608</form13FFileNumber>
          <name>LMCG INVESTMENTS, LLC</name>
        </otherManager>
        <otherManager>
          <cik>0001050470</cik>
          <form13FFileNumber>028-06580</form13FFileNumber>
          <name>LSV ASSET MANAGEMENT</name>
        </otherManager>
        <otherManager>
          <cik>0001435053</cik>
          <form13FFileNumber>028-13124</form13FFileNumber>
          <name>Macquarie Investment Management LTD</name>
        </otherManager>
        <otherManager>
          <cik>0001034182</cik>
          <form13FFileNumber>028-03673</form13FFileNumber>
          <name>MANULIFE INVESTMENT MANAGEMENT (US) LLC</name>
        </otherManager>
        <otherManager>
          <cik>0001419999</cik>
          <form13FFileNumber>028-13243</form13FFileNumber>
          <name>MAR VISTA INVESTMENT PARTNERS LLC</name>
        </otherManager>
        <otherManager>
          <cik>0001279913</cik>
          <form13FFileNumber>028-10682</form13FFileNumber>
          <name>MARATHON ASSET MANAGEMENT LP</name>
        </otherManager>
        <otherManager>
          <cik>0000936944</cik>
          <form13FFileNumber>028-04632</form13FFileNumber>
          <name>MARTINGALE ASSET MANAGEMENT L P</name>
        </otherManager>
        <otherManager>
          <cik>0001465109</cik>
          <form13FFileNumber>028-13573</form13FFileNumber>
          <name>Neuberger Berman Group LLC</name>
        </otherManager>
        <otherManager>
          <cik>0000886982</cik>
          <form13FFileNumber>028-04981</form13FFileNumber>
          <name>GOLDMAN SACHS GROUP INC</name>
        </otherManager>
        <otherManager>
          <cik>0001163368</cik>
          <form13FFileNumber>028-10952</form13FFileNumber>
          <name>PACIFIC INVESTMENT MANAGEMENT CO LLC</name>
        </otherManager>
        <otherManager>
          <cik>0000883677</cik>
          <form13FFileNumber>028-03042</form13FFileNumber>
          <name>PANAGORA ASSET MANAGEMENT INC</name>
        </otherManager>
        <otherManager>
          <cik>0000932859</cik>
          <form13FFileNumber>028-04558</form13FFileNumber>
          <name>PARAMETRIC PORTFOLIO ASSOCIATES LLC</name>
        </otherManager>
        <otherManager>
          <cik>0001454949</cik>
          <form13FFileNumber>028-13350</form13FFileNumber>
          <name>Poplar Forest Capital LLC</name>
        </otherManager>
        <otherManager>
          <cik>0001501436</cik>
          <form13FFileNumber>028-14009</form13FFileNumber>
          <name>QS Investors, LLC</name>
        </otherManager>
        <otherManager>
          <cik>0001768099</cik>
          <form13FFileNumber>028-19339</form13FFileNumber>
          <name>Qtron Investments LLC</name>
        </otherManager>
        <otherManager>
          <cik>0001275893</cik>
          <form13FFileNumber>028-10674</form13FFileNumber>
          <name>RAMIUS ADVISORS LLC</name>
        </otherManager>
        <otherManager>
          <cik>0001520478</cik>
          <form13FFileNumber>028-14481</form13FFileNumber>
          <name>RWC Asset Management LLP</name>
        </otherManager>
        <otherManager>
          <cik>0001056593</cik>
          <form13FFileNumber>028-04691</form13FFileNumber>
          <name>SCHAFER CULLEN CAPITAL MANAGEMENT INC</name>
        </otherManager>
        <otherManager>
          <cik>0001257442</cik>
          <form13FFileNumber>028-11338</form13FFileNumber>
          <name>SSGA FUNDS MANAGEMENT INC</name>
        </otherManager>
        <otherManager>
          <cik>0001061186</cik>
          <form13FFileNumber>028-07104</form13FFileNumber>
          <name>WCM INVESTMENT MANAGEMENT, LLC</name>
        </otherManager>
        <otherManager>
          <cik>0001075869</cik>
          <form13FFileNumber>028-04413</form13FFileNumber>
          <name>Allspring Global Investments, LLC</name>
        </otherManager>
        <otherManager>
          <cik>0001570625</cik>
          <form13FFileNumber>028-21079</form13FFileNumber>
          <name>Perpetual Investment Management Ltd</name>
        </otherManager>
        <otherManager>
          <cik>0001217541</cik>
          <form13FFileNumber>028-10648</form13FFileNumber>
          <name>DIAMOND HILL CAPITAL MANAGEMENT INC</name>
        </otherManager>
        <otherManager>
          <cik>0001508123</cik>
          <form13FFileNumber>028-14178</form13FFileNumber>
          <name>Stone Harbor Investment Partners LP</name>
        </otherManager>
        <otherManager>
          <cik>0001923173</cik>
          <form13FFileNumber>028-22464</form13FFileNumber>
          <name>Leeward Investments, LLC - MA</name>
        </otherManager>
        <otherManager>
          <cik>0001731012</cik>
          <form13FFileNumber>028-18430</form13FFileNumber>
          <name>Alphinity Investment Management Pty Ltd</name>
        </otherManager>
        <otherManager>
          <cik>0000009015</cik>
          <form13FFileNumber>028-00060</form13FFileNumber>
          <name>BARINGS LLC</name>
        </otherManager>
        <otherManager>
          <cik>0001088875</cik>
          <form13FFileNumber>028-04825</form13FFileNumber>
          <name>BAILLIE GIFFORD &amp; CO</name>
        </otherManager>
      </otherManagersInfo>
      <provideInfoForInstruction5>Y</provideInfoForInstruction5>
      <additionalInformation>SEI Investments Company (SEI) is the parent holding company of certain institutional investment managers, as defined by Section 13(f) of the Securities Exchange Act of 1934, as amended (the "Act"). For purposes of the reporting requirements under Section 13(f) of the Act, and the rules promulgated thereunder, SEI does not exercise, and therefore disclaims, investment discretion with respect to any Section 13(f) securities positions over which its investment operating subsidiaries exercise such discretion. To the extent, however, that SEI's ownership interest in such subsidiaries may nevertheless give rise to a Form 13F obligation for SEI, the information required by Form 13F is reported herein on behalf of the following subsidiaries: SEI Investments Management Corporation ("SIMC"), SEI Trust Company and SEI Investments Canada Company (SEI Canada). Voting authority with respect to the Section 13(f) securities reported herein resides with and is exercised by SEI's operating subsidiaries, unless otherwise indicated. Although SEI has not been delegated voting authority over such Section 13(f) securities, and disclaims such voting authority, pursuant to instruction 12b.viii of Form 13F, and for that purpose only, such Section 13(f) securities are reported as "Sole Voting Authority." SIMC and SEI Canada each serve as an investment adviser to a number of pooled investment vehicles, which may include mutual funds, hedge funds, private equity funds, collective investment trusts and offshore investment funds (together, the "Pooled Investment Vehicles"). In addition, SIMC sponsor and may serve as adviser to, separately managed account programs (SMA Programs) . SIMC and SEI Canada may act as a "manager of managers" whereby each retain, subject to SIMC's and SEI Canada's oversight, respectively, sub-advisers to buy and sell securities on behalf of such Pooled Investment Vehicles and SMA Programs. To the extent that SIMC's and SEI Canada's role as a manager of managers could give rise to a Form 13F obligation, SIMC or SEI Canada has instructed its sub-advisers to file a Form 13F with respect to such securities and has included such sub-advisers in the "list of other managers reporting for this manager" below.</additionalInformation>
    </coverPage>
    <signatureBlock>
      <name>Michael N. Peterson</name>
      <title>Executive Vice President</title>
      <phone>610-676-1000</phone>
      <signature>Michael N. Peterson</signature>
      <city>Oaks</city>
      <stateOrCountry>PA</stateOrCountry>
      <signatureDate>11-13-2025</signatureDate>
    </signatureBlock>
    <summaryPage>
      <otherIncludedManagersCount>4</otherIncludedManagersCount>
      <tableEntryTotal>5633</tableEntryTotal>
      <tableValueTotal>92994761394</tableValueTotal>
      <isConfidentialOmitted>false</isConfidentialOmitted>
      <otherManagers2Info>
        <otherManager2>
          <sequenceNumber>2</sequenceNumber>
          <otherManager>
            <cik>0000907692</cik>
            <form13FFileNumber>028-16475</form13FFileNumber>
            <crdNumber>000105146</crdNumber>
            <secFileNumber>801-24593</secFileNumber>
            <name>SEI INVESTMENTS MANAGEMENT CORP</name>
          </otherManager>
        </otherManager2>
        <otherManager2>
          <sequenceNumber>3</sequenceNumber>
          <otherManager>
            <cik>0001204692</cik>
            <form13FFileNumber>028-10297</form13FFileNumber>
            <name>SEI TRUST CO</name>
          </otherManager>
        </otherManager2>
        <otherManager2>
          <sequenceNumber>4</sequenceNumber>
          <otherManager>
            <cik>0001633036</cik>
            <form13FFileNumber>028-16449</form13FFileNumber>
            <name>SEI Investments Canada Co</name>
          </otherManager>
        </otherManager2>
        <otherManager2>
          <sequenceNumber>1</sequenceNumber>
          <otherManager>
            <cik>0001510989</cik>
            <form13FFileNumber>028-14070</form13FFileNumber>
            <crdNumber>000144908</crdNumber>
            <secFileNumber>801-70305</secFileNumber>
            <name>Informed Momentum Co LLC</name>
          </otherManager>
        </otherManager2>
      </otherManagers2Info>
    </summaryPage>
  </formData>
</edgarSubmission>
