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Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
Originator-Key-Asymmetric:
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 TWSM7vrzLADbmYQaionwg5sDW3P6oaM5D3tdezXMm7z1T+B+twIDAQAB
MIC-Info: RSA-MD5,RSA,
 VxcWJH+ryW49I19Rmcf3IamV7h6IYSeS/IV5zHm9ah8R3stHqNxKuNjFbr0fZszu
 InQUF2TYeYml7qkctLZxlw==

<SEC-DOCUMENT>0001246151-05-000049.txt : 20050715
<SEC-HEADER>0001246151-05-000049.hdr.sgml : 20050715
<ACCEPTANCE-DATETIME>20050715172545
ACCESSION NUMBER:		0001246151-05-000049
CONFORMED SUBMISSION TYPE:	3
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20050705
FILED AS OF DATE:		20050715
DATE AS OF CHANGE:		20050715

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			CLEVELAND BRUCE A
		CENTRAL INDEX KEY:			0001333063

	FILING VALUES:
		FORM TYPE:		3
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-20725
		FILM NUMBER:		05958004

	BUSINESS ADDRESS:	
		BUSINESS PHONE:		(650) 477-5000

	MAIL ADDRESS:	
		STREET 1:		2207 BRIDGEPOINTE PARKWAY
		CITY:			SAN MATEO
		STATE:			CA
		ZIP:			94404

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>c0001333063d20050715f3f.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>3</documentType>

    <periodOfReport>2005-07-05</periodOfReport>

    <noSecuritiesOwned>0</noSecuritiesOwned>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001333063</rptOwnerCik>
            <rptOwnerName>CLEVELAND BRUCE A</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O SIEBEL SYSTEMS, INC.</rptOwnerStreet1>
            <rptOwnerStreet2>2207 BRIDGEPOINTE PARKWAY</rptOwnerStreet2>
            <rptOwnerCity>SAN MATEO</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>94404</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>SVP &amp; GM, Products</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>3172</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>123331</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>Cleveland Family Trust</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeHolding>
            <securityTitle>
                <value>Stock Options (Right to buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>7.6</value>
            </conversionOrExercisePrice>
            <exerciseDate>
                <value>2005-07-12</value>
                <footnoteId id="F1"/>
            </exerciseDate>
            <expirationDate>
                <value>2010-08-30</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>500000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeHolding>
        <derivativeHolding>
            <securityTitle>
                <value>Restricted Stock Unit</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>0</value>
            </conversionOrExercisePrice>
            <exerciseDate>
                <value>2009-01-31</value>
                <footnoteId id="F2"/>
            </exerciseDate>
            <expirationDate>
                <value>2009-01-31</value>
                <footnoteId id="F3"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>25000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeHolding>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">20% of the shares subject to the option shall vest on July 12, 2005 and 5% shall vest at the end of each quarter of service thereafter.</footnote>
        <footnote id="F2">100% of the Restricted Stock Unit will vest on January 31, 2009; provided, however, that if certain corporate performance targets are achieved, a portion of such units will accelerate and vest earlier.</footnote>
        <footnote id="F3">The Restricted Stock Unit does not have an expiration date.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>Kimberley E. Henningsen, Power of Attorney</signatureName>
        <signatureDate>2005-07-15</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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