Effects of acid deposition on the acidification of surface water over a short term period were studied during June~October, 1995. A reservoir located in Chunchon, Kangwondo was selected for this study because this reservoir had received little man-made pollutants. Geological survey within the study area was carried out and the pH of a small and shallow stream flowing from the mountain valley down to the reservoir was monitored. Rainfall was measured by using a rain gauge and the precipitation was collected by automatic precipitation sampler. During the study period, rain pH was in the range of 3.81~5.77 with an average of 4.8. The EC was in the range of 5~189$mu$S/cm with an average of 10.6$mu$S/cm. ionic composition of the rainfall showed that of the anions, deposition of ${SO_4}^{2-}$, was highest with 3,119.7 kg/$ extrm{km}^2$, and it was $NH^{4+}$ with 1,053.2kg/$ extrm{km}^2$ for cations. The surface water pHs were maintained neutral or weak basic representing little evidence of acidification regardless of the acidic rainfall pH. Every time of sampling, however, the pHs exhibited increasing tendency as elevation of measuring site of the stream became lowered, which indicated the impacts of acid-base reactions by acidic or basic substances during travel of water downstream. This result suggested the necessity of further research to determine the respective buffering capacity of soil and underlying rocks.