Tree species compositions affect soil physiochemical characteristics, however the effects of transition of tree species at the same forests are relatively unknown. This study was conducted to determine soil characteristics such as pH, CEC and CN ratio affected by the tree species composition in central Korea forests. To investigate the characteristics on mineral soils in common Korean tree species (pine-50-60-year-old Pinus densiflora, oak-40-50-year-old Quercus spp.), five 40m X 40m plots were chosen in natural forests in Gwangneung Experimental Forests based on the basal area of all trees over than 5cm DBH: one of 100% of pine [pure pine], three of 70, 50 and 40% of pine and 30, 50 and 60% of oak trees [mixed pine-oak], and 90% of oak trees [pure oak]. A total of 75 soil samples were collected from the study stands to depths of 0-30cm. Soil pH, CEC and CN ratio significantly decreased on increase in portion of oak trees in study stands. This result showed that soil acidification, CEC and CN ratio might be increased with changing tree composition from pine to oak trees.