The Chungryang-stream is one of the tributaries of the Han-river which flows through the north-eastern part of Seoul city which is the largest one in Korea. The total length of the stream is 102.2 kilometers (main stream: 42.2 kilometers, its branch: 60 kilometers) and the study area is about 239 square kilometers with the population of 1.8 million. Major sources of pollution on the stream in study area are both of industrial and domestic waste water, which adversely affect the water quality of the down stream of the Han-river. The water quality measured by BOD_5 of the upstream of Chungryang-stream was about 7.0 milligrams per liter. However passing through the area of the Euijungbu, the water quality measured by BOD_5 was showing high concentration as about 40 milligrams per, liter due to the sewage from the Euijungbu city and the highly polluted water of Paeksuk-stream. No significant seasonal changes in DO concentration are shown in main stream except upstream and the ratio of T. coli/F. coli is 3. 4 in the upstream, 1. 6 in the midstream and 2.3 in the downstream. COD values of sediments range from 3. 0 to 384. 9 milligrams per liter and it is found a wide viriation of the values owing to the rainfall.