-----BEGIN PRIVACY-ENHANCED MESSAGE-----
Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
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MIC-Info: RSA-MD5,RSA,
 PNO4QpbZM/FJZTQbx6FF+Vgz7GP+Bp6yO/FSUanSkMSRjxZOYz/q9vJ0gcVwBQO8
 YD5qtoRdKnuv/hWFT1C4dw==

<SEC-DOCUMENT>0001049502-03-000015.txt : 20030702
<SEC-HEADER>0001049502-03-000015.hdr.sgml : 20030702
<ACCEPTANCE-DATETIME>20030701181041
ACCESSION NUMBER:		0001049502-03-000015
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20030701
FILED AS OF DATE:		20030702

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			MKS INSTRUMENTS INC
		CENTRAL INDEX KEY:			0001049502
		STANDARD INDUSTRIAL CLASSIFICATION:	INDUSTRIAL INSTRUMENTS FOR MEASUREMENT, DISPLAY, AND CONTROL [3823]
		IRS NUMBER:				042277512
		STATE OF INCORPORATION:			MA
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		SIX SHATTUCK RD
		CITY:			ANDOVER
		STATE:			MA
		ZIP:			01810
		BUSINESS PHONE:		9789752350

	MAIL ADDRESS:	
		STREET 1:		SIX SHATTUCK ROAD
		CITY:			ANDOVER
		STATE:			MA
		ZIP:			01810

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			SMITH DONALD K
		CENTRAL INDEX KEY:			0000922832

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-23621
		FILM NUMBER:		03769131

	BUSINESS ADDRESS:	
		STREET 1:		6 SHATTUCK ROAD
		STREET 2:		C/O MKS INSTRUMENTS
		CITY:			ANDOVER
		STATE:			MA
		ZIP:			01810
		BUSINESS PHONE:		9789752350

	MAIL ADDRESS:	
		STREET 1:		6 SHATTUCK ROAD
		STREET 2:		C/O MKS INSTRUMENTS
		CITY:			ANDOVER
		STATE:			MA
		ZIP:			01810

	FORMER NAME:	
		FORMER CONFORMED NAME:	DONALD K SMITH
		DATE OF NAME CHANGE:	19940506
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>smi74.xml
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>
    <schemaVersion>X0101</schemaVersion>

    <documentType>4</documentType>
	<periodOfReport>2003-07-01</periodOfReport>
	<notSubjectToSection16>0</notSubjectToSection16>
    <issuer>
        <issuerCik>0001049502</issuerCik>
        <issuerName>MKS INSTRUMENTS INC</issuerName>
        <issuerTradingSymbol>MKSI</issuerTradingSymbol>
	</issuer>
	<reportingOwner>
		<reportingOwnerId>
            <rptOwnerCik>0000922832</rptOwnerCik>
            <rptOwnerName>SMITH DONALD K</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>  </rptOwnerStreet1>
            <rptOwnerStreet2>  </rptOwnerStreet2>
            <rptOwnerCity>  </rptOwnerCity>
            <rptOwnerState>  </rptOwnerState>
            <rptOwnerZipCode>  </rptOwnerZipCode>
        </reportingOwnerAddress>
            <reportingOwnerRelationship>
			<isDirector>0</isDirector>
			<isOfficer>1</isOfficer>
			<isTenPercentOwner>0</isTenPercentOwner>
			<isOther>0</isOther>
			<officerTitle>V.P. &amp; CTO</officerTitle>
		</reportingOwnerRelationship>
	</reportingOwner>
	<derivativeSecurity>
		<securityTitle>
			<value>Stock Option (Right to Buy)</value>
		</securityTitle>
		<conversionOrExercisePrice>
			<value>17.60</value>
		</conversionOrExercisePrice>
		<transactionDate>
			<value>2003-07-01</value>
		</transactionDate>
		<transactionCoding>
			<transactionFormType>4</transactionFormType>
			<transactionCode>A</transactionCode>
			<equitySwapInvolved>0</equitySwapInvolved>
		</transactionCoding>
		<transactionAmounts>
			<transactionShares>
				<value>635</value>
			</transactionShares>
			<transactionValue>
				<value>0</value>
			</transactionValue>
			<transactionAcquiredDisposedCode>
				<value>A</value>
			</transactionAcquiredDisposedCode>
		</transactionAmounts>
		<exerciseDate>
			<value>1988-08-08</value>
		</exerciseDate>
		<expirationDate>
			<value>2013-07-01</value>
		</expirationDate>
		<underlyingSecurity>
			<underlyingSecurityTitle>
				<value>Common</value>
			</underlyingSecurityTitle>
			<underlyingSecurityShares>
				<value>635</value>
			</underlyingSecurityShares>
		</underlyingSecurity>
		<postTransactionAmounts>
			<sharesOwnedFollowingTransaction>
				<value>635</value>
				<footnoteId id="F1"/>
			</sharesOwnedFollowingTransaction>
		</postTransactionAmounts>
		<ownershipNature>
			<directOrIndirectOwnership>
				<value>D</value>
			</directOrIndirectOwnership>
			<natureOfOwnership>
				<value/>
			</natureOfOwnership>
		</ownershipNature>
	</derivativeSecurity>
	<footnotes>
		<footnote id="F1">Beneficial Holdings derivative securities 130,222.</footnote>
	</footnotes>
	<ownerSignature>
		<signatureName>By: POA on file</signatureName>
		<signatureDate>2003-07-01</signatureDate>
	</ownerSignature>
</ownershipDocument>

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