The vegetation on Yakushima Island, Japan, occurs on soils derived from Akahoya volcanic ash, released from the Kikai Caldera about 7,300 years ago. We examined the magnitude of the contribution of the minerals derived from the volcanic ash to the current nutrient pool/dynamics of the forest ecosystems of Yakushima Island. We focused on Ca, Mg and phosphorus (P), both of which are derived from parent materials, by using strontium and lead stable isotope ratios (⁸⁷Sr/⁸⁶Sr and ²⁰⁸Pb/²⁰⁷Pb), which are widely used to estimate chemical weathering and soil genesis. We measured ⁸⁷Sr/⁸⁶Sr and ²⁰⁸Pb/²⁰⁷Pb of parent rocks, volcanic ash, and rain, which were considered as source of nutrients, and also those of topsoils and plants. We determined how each endmember contributed to soil and plant nutrients based on the mixing ratio of the three endmember isotope ratios. The contribution rate of volcanic ash for soil extractable Ca and Mg ranged from 3.4 to 53.7 % and decreased with increasing elevation. The contribution rate of volcanic ash for soil total P, which was estimated by eliminating the effects of rain, declined with increasing elevation, significantly positively correlated with the concentration of secondary amorphous minerals derived from volcanic ash (i.e., soil Alo + 1/2Feo), and marginally significantly positively correlated with soil total P. These results suggest that contribution rates for soil Ca, Mg and P derived from deposited volcanic ash decline with increasing elevation probably reflecting the past weathering/erosion process which increases with elevation.