Effects of forestry on soil properties, stream water chemistry and mass balance in watersheds had been confieremed by many previous studies. However, they have not clarified in detail variation processes of soil chemistry and soil physics after the hinoki and larch forestation. To clarify the variation processes, it is important to confirm the difference of soil chemistry and soil physics on the artifitial and natural forest. In this research, we conducted the soil physical and chemical investigations on seven slopes covered by hinoki (chamecyparis obtusa) and larch (Larix leptolepis) artificial and beech (Fagus crenata) natural forest in a highland area, the western side of Tokyo. The water repellency of A_0 horizon was stronger on the artificial forest slope than on the natural forest. In addition, the permeability was low on the artificial forest due to the strong water repellency. On the artificial forest, both of the exchangeable base cation content and soil pH were low and Al<^3+> concentration was high, as compared with those on the natural forest. These results suggest that the soil acidification is progressed on the artificial forest. The decline of soil pH by the forestation was controlled by the increase of H^+ supply at the A_0 horizon due to the property of litter decomposition and the decrease of base cation supply at the A-horizon. In general, the cation supply rate such as weathering rate is controlled by the infiltration rate and temperature. These soil physical and chemical properties suggest that infitration rate at the A-horizon. declines after the forestation, weathering rate declines and consequently soil is acidified.