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Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
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<SEC-DOCUMENT>0001140361-07-012760.txt : 20070621
<SEC-HEADER>0001140361-07-012760.hdr.sgml : 20070621
<ACCEPTANCE-DATETIME>20070621160902
ACCESSION NUMBER:		0001140361-07-012760
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20070619
FILED AS OF DATE:		20070621
DATE AS OF CHANGE:		20070621

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			MCCLOY JOHN J II
		CENTRAL INDEX KEY:			0001263780

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-27432
		FILM NUMBER:		07934070

	MAIL ADDRESS:	
		STREET 1:		20 KETCHUM STREET
		CITY:			WESTPORT
		STATE:			CT
		ZIP:			06880

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			CLEAN DIESEL TECHNOLOGIES INC
		CENTRAL INDEX KEY:			0000949428
		STANDARD INDUSTRIAL CLASSIFICATION:	INDUSTRIAL INORGANIC CHEMICALS [2810]
		IRS NUMBER:				061393453
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		300 ATLANTIC ST
		STREET 2:		STE 702
		CITY:			STAMFORD
		STATE:			CT
		ZIP:			06901
		BUSINESS PHONE:		2033277050

	MAIL ADDRESS:	
		STREET 1:		300 ATLANTIC ST
		STREET 2:		STE 702
		CITY:			STAMFORD
		STATE:			CT
		ZIP:			06901
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>doc1.xml
<DESCRIPTION>FORM 4
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2007-06-19</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000949428</issuerCik>
        <issuerName>CLEAN DIESEL TECHNOLOGIES INC</issuerName>
        <issuerTradingSymbol>CLDS</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001263780</rptOwnerCik>
            <rptOwnerName>MCCLOY JOHN J II</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>300 ATLANTIC STREET</rptOwnerStreet1>
            <rptOwnerStreet2>SUITE 702</rptOwnerStreet2>
            <rptOwnerCity>STAMFORD</rptOwnerCity>
            <rptOwnerState>CT</rptOwnerState>
            <rptOwnerZipCode>06901</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
                <footnoteId id="F1"/>
            </securityTitle>
            <transactionDate>
                <value>2007-06-19</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>737</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>10.169</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>7444</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeHolding>
            <securityTitle>
                <value>Option</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>1.02</value>
            </conversionOrExercisePrice>
            <exerciseDate>
                <value>2005-12-20</value>
            </exerciseDate>
            <expirationDate>
                <value>2015-12-20</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>15000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>15000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeHolding>
        <derivativeHolding>
            <securityTitle>
                <value>Option</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>1.575</value>
            </conversionOrExercisePrice>
            <exerciseDate>
                <value>2005-06-09</value>
            </exerciseDate>
            <expirationDate>
                <value>2015-06-09</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>50000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>50000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeHolding>
        <derivativeHolding>
            <securityTitle>
                <value>Stock Option</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>1.82</value>
            </conversionOrExercisePrice>
            <exerciseDate>
                <value>2007-01-04</value>
            </exerciseDate>
            <expirationDate>
                <value>2017-01-04</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>25000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>25000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeHolding>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Amount of Securities Beneficially Owned Following Transaction in Table I  is different from last Form 4 as a result of a reverse split on June 15, 2007.  Change in holdings dated June 19, 2007 in Table I is stated as a post-split amount and represents shares in lieu of director's fees for the 1st quarter 2007 valued on the average of high and low share prices over the period.  The derivative securities in Table II have not been restated to reflect the reverse split.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>John J McCloy, II</signatureName>
        <signatureDate>2007-06-21</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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