The Chennai also called as Detroit of India due to its Automotive Industry presence producing over 40% of the India's Vehicle and Components. During 2001-02, the Chennai Automotive Industry Cluster(CAIC) consists of Ambattur, Thirumalizai and Thirumudivakkam Industrial Estate located in Chennai had faced problems on infrastructure, technology, procurement, production and marketing. During diagnostic study it is found that there is need for Cluster Development Approach(CDA) for these Industries. The objective is to study on the Impact Assessment of Chennai Automotive Industry Cluster before (2001-02) and after the CDA (2008-09). The methodology adopted is collection of primary data from 100 ACI using qualitative questionnaire and analysing using UNIDO Methodology of Impact Assessment. To conclude In Firm Level Impact Assessment, Association / Network Level Impact Assessment and the Cluster Level Impact assessment is high when all the three locations like Ambattur, Thirumudivakkam and Thirumalisai Industrial Estate are taken into account & the units are exporting their products to North America, South America, Europe, Australia, Africa & Asia after the Cluster Development Approach