To investigate the variations of physico-chemical factors and microbial population, in ten stations at water region of coastal area of Chagwi-Do, Nutritive salts, water temperature, transparency, suspended solid, salinity, COD, DO, pH, heterotrophic bacteria, coliform group and Vibrio spp. were analysed three times in September, November in 2004 and February in 2005. Heterotrophic bacteria in surface water was 3.5×101～1.16×103 cfu/ml, 1.0×102～5.2×101 cfu/ml, 2.0×101～7.6×101 and bottom water counted 7.0×102～1.0×103 cfu/ml, 1.4×101～2.5×102 cfu/ml, 2.0×102～4.2×101 cfu/ml in September, November in 2004 and February in2005, respectively. The cell number of total coliform bacteria in the surface water amounted to 0～4.3×102 cfu/ml, 0～6.0×101 cfu/ml, 0～1.0×101 cfu/ml and bottom water amounted 0～2.2×102 cfu/ml, 0～5.4×102 cfu/ml, 0～2.0×101 cfu/ml in September, November in 2004 and February in 2005, respectively. As for Vibrio spp., the cell number in the surface water was 1.0×101～2.5×102 cfu/ml, 1.0×101～2.0×101 cfu/ml, 0 cfu/㎖ and bottom water counted 1.0×101～5.2×102 cfu/ml, 0 cfu/㎖, 2.0×101 cfu/ml in September, November in 2004 and February in 2005, respectively.