Plants in karst soils generally grow under phosphorus (P) deficient conditions since calcium (Ca) ions in the soil deposits phosphate under high pH (> 7.5-8.0). However, little is known about the characteristics of soils and functional traits of trees in karst forests with relatively low soil pH. Japanese karst soils are known to have relatively low soil pH, probably because of high precipitation. We hypothesized that the effect of P deficiency is weak in the karst soil with relatively low pH. We investigated soil properties and nutrient concentrations of leaves of four dominant trees (Carpinus tschonoskii, Cornus macrophylla, Neolitsea sericea, and Quercus variabilis) and leaf litter on the forest floor in karst and neighboring non-karst (sandstone) forests on Mt. Ibuki, Japan. Soil pH of the karst and non-karst sites were 6.5 and 5.6. The higher Ca and P and lower potassium availabilities were shown in the karst soil than the non-karst soil. P concentrations of leaf and leaf litter were also higher in the karst site. Our results suggest that karst soil could release much P after soil pH decreased by weathering.