The National Park should be preserved as described in the regulation. However, the development has resulted in degrading the environment in the park. Especially, the collective facility area has been developed for the commercial benefit rather than for the preservation. So, it is necessary to figure out the impact of the development plan proposed. Thus, the purpose of this study is to explore the hydrologic effects due to the collective facility area development in the National Park. The study site is the second collective facility area of Mt. Kyeryong National Park. The analysis of hydrologic effects due to the development has been carried out using the GIS in this study. The Rational Method and Soil Conservation Service(SCS) were used to estimate the runoff volume. During this procedure, GIS software, ARC/INFO was used to integrate, manipulate, and calculate the attribute value of a number of ploygons which represen each land use characteristic. A program was written to compute the attribute value of each polygon and to estimate the difference of peaktime runoff volume before and after development.