This survey was carried out to evaluate offshore water quality to Western sea in Korea by bioassay using early development system of Asterias amurensis. Despite of the inflows of several river systems, most West coast maintained the grade Ⅱ water quality because embryo development of Asterias amurensis was moderately inhibited. This is thought to be due to the decrease in pollutant input resulting from the purification of inflow rivers (e. g., the control of waste water discharge and the construction of sewage treatment facilities), and the dilution of pollutants by a strong tidal mixing with a large difference between the ebb and flood tides. However, the water quality of Asan, Hampu˘ng and Choˇnsu Bays, where circulations of water are relatively poor, and Kunsan and Mokpo harbors which are influenced by pollutants from neighboring cities have shown the grade III because embryo development of Asterias amurensis was strongly inhibited.