-----BEGIN PRIVACY-ENHANCED MESSAGE-----
Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
Originator-Key-Asymmetric:
 MFgwCgYEVQgBAQICAf8DSgAwRwJAW2sNKK9AVtBzYZmr6aGjlWyK3XmZv3dTINen
 TWSM7vrzLADbmYQaionwg5sDW3P6oaM5D3tdezXMm7z1T+B+twIDAQAB
MIC-Info: RSA-MD5,RSA,
 Cg9xYYoroN+XRpjV2joYUQnhf+zbbkLf89wdRCXCnyrX4QR9hKOitK1eInIsp4oU
 LbCp6AsfFa1dpOkAs0kkGA==

<SEC-DOCUMENT>0001179110-04-009162.txt : 20040429
<SEC-HEADER>0001179110-04-009162.hdr.sgml : 20040429
<ACCEPTANCE-DATETIME>20040429150527
ACCESSION NUMBER:		0001179110-04-009162
CONFORMED SUBMISSION TYPE:	3
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20040428
FILED AS OF DATE:		20040429

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			CASEY DONALD P
		CENTRAL INDEX KEY:			0001193372

	FILING VALUES:
		FORM TYPE:		3
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-24786
		FILM NUMBER:		04764524

	MAIL ADDRESS:	
		STREET 1:		1310 RIDDER PARK DR
		CITY:			SAN JOSE
		STATE:			CA
		ZIP:			95131-2313

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			ASPEN TECHNOLOGY INC /DE/
		CENTRAL INDEX KEY:			0000929940
		STANDARD INDUSTRIAL CLASSIFICATION:	SERVICES-COMPUTER PROGRAMMING SERVICES [7371]
		IRS NUMBER:				042739697
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			0630

	BUSINESS ADDRESS:	
		STREET 1:		TEN CANAL PARK
		CITY:			CAMBRIDGE
		STATE:			MA
		ZIP:			02141
		BUSINESS PHONE:		6179491000

	MAIL ADDRESS:	
		STREET 1:		TEN CANAL PARK
		CITY:			CAMBRIDGE
		STATE:			MA
		ZIP:			02141
</SEC-HEADER>
<DOCUMENT>
<TYPE>3
<SEQUENCE>1
<FILENAME>edgar.xml
<DESCRIPTION>FORM 3 -
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>3</documentType>

    <periodOfReport>2004-04-28</periodOfReport>

    <noSecuritiesOwned>1</noSecuritiesOwned>

    <issuer>
        <issuerCik>0000929940</issuerCik>
        <issuerName>ASPEN TECHNOLOGY INC /DE/</issuerName>
        <issuerTradingSymbol>AZPN</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001193372</rptOwnerCik>
            <rptOwnerName>CASEY DONALD P</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O ASPEN TECHNOLOGY, INC.</rptOwnerStreet1>
            <rptOwnerStreet2>10 CANAL PARK</rptOwnerStreet2>
            <rptOwnerCity>CAMBRIDGE</rptOwnerCity>
            <rptOwnerState>MA</rptOwnerState>
            <rptOwnerZipCode>02141</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable></nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes></footnotes>

    <ownerSignature>
        <signatureName>/s/ Donald P. Casey</signatureName>
        <signatureDate>2004-04-29</signatureDate>
    </ownerSignature>
</ownershipDocument>

</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
-----END PRIVACY-ENHANCED MESSAGE-----