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Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
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MIC-Info: RSA-MD5,RSA,
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 cK5TfmxgRgRvBYvYMvUnpg==

<SEC-DOCUMENT>0001209191-06-045515.txt : 20060811
<SEC-HEADER>0001209191-06-045515.hdr.sgml : 20060811
<ACCEPTANCE-DATETIME>20060811115908
ACCESSION NUMBER:		0001209191-06-045515
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20060809
FILED AS OF DATE:		20060811
DATE AS OF CHANGE:		20060811

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			DIDONATO EUGENE
		CENTRAL INDEX KEY:			0001180465

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-21319
		FILM NUMBER:		061023675

	BUSINESS ADDRESS:	
		STREET 1:		150 SHAW ROAD
		CITY:			CHESTNUT HILL
		STATE:			MA
		ZIP:			02467
		BUSINESS PHONE:		7813594201

	MAIL ADDRESS:	
		STREET 1:		150 SHAW ROAD
		CITY:			CHESTNUT
		STATE:			MA
		ZIP:			02467

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			LIGHTBRIDGE INC
		CENTRAL INDEX KEY:			0001017172
		STANDARD INDUSTRIAL CLASSIFICATION:	RADIO TELEPHONE COMMUNICATIONS [4812]
		IRS NUMBER:				043065140
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		30 CORPORATE DRIVE
		CITY:			BURLINGTON
		STATE:			MA
		ZIP:			01803
		BUSINESS PHONE:		7813594000

	MAIL ADDRESS:	
		STREET 1:		30 CORPORATE DRIVE
		CITY:			BURLINGTON
		STATE:			MA
		ZIP:			01803
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>doc4.xml
<DESCRIPTION>FORM 4 SUBMISSION
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2006-08-09</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001017172</issuerCik>
        <issuerName>LIGHTBRIDGE INC</issuerName>
        <issuerTradingSymbol>LTBG</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001180465</rptOwnerCik>
            <rptOwnerName>DIDONATO EUGENE</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>150 SHAW ROAD</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>BROOKLINE</rptOwnerCity>
            <rptOwnerState>MA</rptOwnerState>
            <rptOwnerZipCode>02467</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>VP and General Counsel</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2006-08-09</value>
            </transactionDate>
            <deemedExecutionDate>
                <value>2006-08-09</value>
            </deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>F</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>203</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>11.23</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>9797</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes></footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Eugene DiDonato</signatureName>
        <signatureDate>2006-08-11</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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