The synthetic detergent residuals in Han River were determined at seven areas near Seoul, in the drought season, Juley, in the rainy season, August and winter, November 1972. At the survey in July, 2 areas, Chung Gae River area and An Yang River area, were found to contain above 0.5ppm of synthetic detergents residuals. The other 4 areas, Duck So, Dukk Do, Bo Guang Dong, Ma Pho and Nan Ji Islet area, were less than 0.5ppm. In August, all seven areas were found to contain below 0.5ppm. In November, 4 areas, Chung Gae River, An Yang River, Ma Pho and Nan Ji Islet area were found to contain above 0.5ppm of synthetic detergent residuals, and 2 areas, Duck So and Dukk Do area were below 0.5ppm.