-----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,
 Hdt0CFoFodjuvaqWtaAJkdDQsKUPJpNRNsXboYthM0gjs7GuAXcJBniUZlS/7z8+
 RNyLOstTlHLTo4u/NSkntA==

<SEC-DOCUMENT>0001328980-06-000001.txt : 20060926
<SEC-HEADER>0001328980-06-000001.hdr.sgml : 20060926
<ACCEPTANCE-DATETIME>20060926144249
ACCESSION NUMBER:		0001328980-06-000001
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20060922
FILED AS OF DATE:		20060926
DATE AS OF CHANGE:		20060926

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			GSI GROUP INC
		CENTRAL INDEX KEY:			0001076930
		STANDARD INDUSTRIAL CLASSIFICATION:	MISCELLANEOUS ELECTRICAL MACHINERY, EQUIPMENT & SUPPLIES [3690]
		IRS NUMBER:				980110412
		STATE OF INCORPORATION:			A3
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		39 MANNING ROAD
		STREET 2:		.
		CITY:			BILLERICA
		STATE:			MA
		ZIP:			01821
		BUSINESS PHONE:		978-439-5511

	MAIL ADDRESS:	
		STREET 1:		39 MANNING ROAD
		STREET 2:		.
		CITY:			BILLERICA
		STATE:			MA
		ZIP:			01821

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	GSI LUMONICS INC
		DATE OF NAME CHANGE:	19990401

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	GSI LUMONICS
		DATE OF NAME CHANGE:	19990331

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	LUMONICS INC
		DATE OF NAME CHANGE:	19990115

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			Hatsopoulos Marina
		CENTRAL INDEX KEY:			0001328980

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-25705
		FILM NUMBER:		061108478

	BUSINESS ADDRESS:	
		BUSINESS PHONE:		978-439-5511

	MAIL ADDRESS:	
		STREET 1:		39 MANNING ROAD
		CITY:			BILLERICA
		STATE:			MA
		ZIP:			01821
</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>2006-09-22</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001076930</issuerCik>
        <issuerName>GSI GROUP INC</issuerName>
        <issuerTradingSymbol>GSIG</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001328980</rptOwnerCik>
            <rptOwnerName>Hatsopoulos Marina</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>39 MANNING ROAD</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>BILLERICA</rptOwnerCity>
            <rptOwnerState>MA</rptOwnerState>
            <rptOwnerZipCode>01821</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2006-09-22</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>5400</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>9.26</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>5400</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">The restricted shares vest in three equal annual installments beginning on September 22, 2007.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>Marina Hatsopoulos</signatureName>
        <signatureDate>2006-09-26</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
-----END PRIVACY-ENHANCED MESSAGE-----