With the rapid industrialization and urbanization in recent, the estuarine and coastal regions aorund have been sevely damaged. Han River estuary and Gyeonggi Bay are characterized by high-tidal range and wide tidal flats, a series of reclamation of tidal flat regions and a series of bank construction of inlet regions have been made for industrial, agricultural and new-town building objects. As iIt is necessary to estimate the effect of the past human activities and to assess the cumulative environment change to the future development in the Han River estuary and Gyeonggi bay. As increase of public concern on environmental conservation, the project on retoration technologies for estuaries and coastal seas was started. This study investigated spatial-temporal distribution of water quality in the Han River estuary and Gyeonggi Bay.