-----BEGIN PRIVACY-ENHANCED MESSAGE-----
Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
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MIC-Info: RSA-MD5,RSA,
 R4ox9p7bYtLOuyRXTtsRCQe7ek8FTgh42Za3HGRQCjAw/KEr/dY4Dz0iNrcPxZ6T
 uIRBwpWFAUG+HyGp1gkKWw==

<SEC-DOCUMENT>0001243119-06-000001.txt : 20060913
<SEC-HEADER>0001243119-06-000001.hdr.sgml : 20060913
<ACCEPTANCE-DATETIME>20060913192038
ACCESSION NUMBER:		0001243119-06-000001
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20060912
FILED AS OF DATE:		20060913
DATE AS OF CHANGE:		20060913

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			OPNET TECHNOLOGIES INC
		CENTRAL INDEX KEY:			0001108924
		STANDARD INDUSTRIAL CLASSIFICATION:	SERVICES-PREPACKAGED SOFTWARE [7372]
		IRS NUMBER:				521483235
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			0331

	BUSINESS ADDRESS:	
		STREET 1:		7255 WOODMONT AVENUE
		CITY:			BETHESDSA
		STATE:			MD
		ZIP:			20814
		BUSINESS PHONE:		2404973000

	MAIL ADDRESS:	
		STREET 1:		7255 WOODMONT AVENUE
		CITY:			BETHESDA
		STATE:			MD
		ZIP:			20814

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			FINN STEVEN G
		CENTRAL INDEX KEY:			0001243119

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-30931
		FILM NUMBER:		061089373

	BUSINESS ADDRESS:	
		STREET 1:		C/O OPNET TECHNOLOGIES INC
		STREET 2:		7255 WOODMONT AVE
		CITY:			BETHESDA
		STATE:			MD
		ZIP:			20814
		BUSINESS PHONE:		2404973000

	MAIL ADDRESS:	
		STREET 1:		7255 WOODMONT AVE
		CITY:			BETHESDA
		STATE:			MD
		ZIP:			20814
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>primary_doc.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2006-09-12</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001108924</issuerCik>
        <issuerName>OPNET TECHNOLOGIES INC</issuerName>
        <issuerTradingSymbol>OPNT</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001243119</rptOwnerCik>
            <rptOwnerName>FINN STEVEN G</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>7255 WOODMONT AVE</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>BETHESDA</rptOwnerCity>
            <rptOwnerState>MD</rptOwnerState>
            <rptOwnerZipCode>20814</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Stock Option (Right to Buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>13.25</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2006-09-12</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>10000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>13.25</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F1"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F2"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>10000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>10000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">The option vests in full on the date of the Issuer's Annual Meeting of Stockholders next following the Option Grant Date.</footnote>
        <footnote id="F2">The option expires on the earliest of: i) seven years after the Option Grant Date, ii) 30 days after the Reporting Person ceases to serve as a director of the Issuer, or iii) if serving as a director on the date of death, the first anniversary of the date of death.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>Steven G. Finn by Dennis R. McCoy under Power of Attorney</signatureName>
        <signatureDate>2006-09-13</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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