In order to analyze the water quality variation of surface water around the Sudokwon landfill site, seasonal variations of water temperature, pH, DO, BOD, COD, SS, NH_3-N. NO_2-N, and NO_3-N were examined at 10 sites from January to December, 1996. It was found that the estimates of COD, DO, SS, and NH_3-N were increased compared with the results of environmental impact assessment carried out in 1988. Higher estimates of COD, DO, and SS were due to industrial and agricultural wastewater, and the increase of NH_3-N at Jangdo reservoir site was due to the leachate from the landfill. In particular, the estimate of SS was found to be increased by the soil wash from the landfill during the heavy rainy days.