Environmental monitoring system has been adopted and supplemented as inspection measures for the quantitative and qualitative changes of environmental impact assessment (EIA). Meanwhile it has been continuously pointed out that there is insufficient connection between environmental monitoring system and EIA. Often the agreed environmental impact assessment has not been fulfilled due to the argument of the cost, timing and situations of construction sites. Thus the purpose of this study is in search of the rationalized environmental monitoring system in order to harmonize the development and environmental conservation through the improvement of unreasonable aspects of the current EIA execution process. As to comply with the purpose, this research was carried out with three different but complimentary sources: environmental laws and regulations, foreign case studies of Japan, U.S.A. and Canada, and interviews with 73 experts. Finally, improved environmental monitoring system has been introduced reflecting the present process of EIA.