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Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
Originator-Key-Asymmetric:
 MFgwCgYEVQgBAQICAf8DSgAwRwJAW2sNKK9AVtBzYZmr6aGjlWyK3XmZv3dTINen
 TWSM7vrzLADbmYQaionwg5sDW3P6oaM5D3tdezXMm7z1T+B+twIDAQAB
MIC-Info: RSA-MD5,RSA,
 UKs5QoUGFQRn3kKJBNrlIxzzKrxY4FyD1mtqOIp+WhJGqHGI0s527X9+mLsS/9CP
 rCqpoZ1gP+bzCIyF5gkhFg==

<SEC-DOCUMENT>0001246151-04-000068.txt : 20040810
<SEC-HEADER>0001246151-04-000068.hdr.sgml : 20040810
<ACCEPTANCE-DATETIME>20040810183714
ACCESSION NUMBER:		0001246151-04-000068
CONFORMED SUBMISSION TYPE:	3
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20040801
FILED AS OF DATE:		20040810

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			McPartland Eileen
		CENTRAL INDEX KEY:			0001299822

	FILING VALUES:
		FORM TYPE:		3
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-20725
		FILM NUMBER:		04965493

	BUSINESS ADDRESS:	
		BUSINESS PHONE:		6504775000

	MAIL ADDRESS:	
		STREET 1:		C/O SIEBEL SYSTEMS, INC.
		STREET 2:		51 JFK PARKWAY
		CITY:			SHORT HILLS
		STATE:			NJ
		ZIP:			07078

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			SIEBEL SYSTEMS INC
		CENTRAL INDEX KEY:			0001006835
		STANDARD INDUSTRIAL CLASSIFICATION:	SERVICES-PREPACKAGED SOFTWARE [7372]
		IRS NUMBER:				943187233
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		2207 BRIDGEPOINTE PARKWAY
		CITY:			SAN MATEO
		STATE:			CA
		ZIP:			94404
		BUSINESS PHONE:		6504775000

	MAIL ADDRESS:	
		STREET 1:		2207 BRIDGEPOINTE PARKWAY
		CITY:			SAN MATEO
		STATE:			CA
		ZIP:			94404
</SEC-HEADER>
<DOCUMENT>
<TYPE>3
<SEQUENCE>1
<FILENAME>c0001299822d20040810f3f.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>3</documentType>

    <periodOfReport>2004-08-01</periodOfReport>

    <noSecuritiesOwned>1</noSecuritiesOwned>

    <issuer>
        <issuerCik>0001006835</issuerCik>
        <issuerName>SIEBEL SYSTEMS INC</issuerName>
        <issuerTradingSymbol>SEBL</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001299822</rptOwnerCik>
            <rptOwnerName>McPartland Eileen</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O SIEBEL SYSTEMS, INC.</rptOwnerStreet1>
            <rptOwnerStreet2>51 JFK WAY</rptOwnerStreet2>
            <rptOwnerCity>SHORT HILLS</rptOwnerCity>
            <rptOwnerState>NJ</rptOwnerState>
            <rptOwnerZipCode>07078</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>SVP, Global Services</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable></nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes></footnotes>

    <ownerSignature>
        <signatureName>Eileen J McPartland</signatureName>
        <signatureDate>2004-08-10</signatureDate>
    </ownerSignature>
</ownershipDocument>

</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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