This research was conducted to investigate the influential factors of the runoff of water and hillslope erosion caused by the large - scale harvesting operation. It was carried out on harvested sites (13㏊) and non - harvested sites(13㏊) in Seoul National University Research Forest [(Mt.) Paekunsan] , from 1993 to 1994. 1. The amount of runoff of water was increased as the unit of rainfall increases, and the amount of runoff on harvested sites was larger than that of non - harvested sites by 28% in the first year and 24.5% in the second year after harvesting. According to the multiple regression equation for surface runoff, unit and number of rainfall, amount of hillslope erosion and soil bulk density showed statistically significance(R²=0.91). 2. The amount of hillslope erosion on harvested sites was larger than that of non - harvested sites by 7 times during the first year of harvesting and 2 times during the second year. 3. The multiple regression equations for hillslope erosion showed that soil bulk density, surface runoff of water and unit of rainfall(these factors were not controllable) had statistically significance(R²=0.74). 4. Soil runoff in harvested and non harvested sites were maximum 6.7% and 1% of the amount of hillslope erosion, respectively during the first year of harvesting. And the second year of harvesting soil runoff in harvested and non harvested cites were maximum 5.7% and 1.9%of the amount of hillslope erosion. From the above results, when in planning for timber harvesting, the buffer strip - woods zone must be remained to diminish soil and water runoff and to preserve water quality.