This paper attempt; to analyze the institutionalization process of Environmental Impact Assessment(EIA) system within the context of Korean environmental policy. The implementation of EIA in the 1980`s was not seriously considered by other government agencies and was sometimes degraded as mere formality due to the inherent problems of the system. With viewing the theory and practice of EIA in Korea, this paper argues that it is essential to reinforce ex post facto management of EIA, incorporate the participation of residents of concerned areas, upgrade the validity of assessment by selecting a credible assessment-agenices and develop the required technologies. Finally, this paper acknowledge the necessity of devising the mechanism to reconcile the conflict between the regional interest and the national interest.