δ15N in leaves and soil were investigated in Japanese cedar (Cryptomeria japonica) and hinoki cypress (Chamaecyparis obtusa) plantations along a precipitation gradient in Shikoku district,southern Japan.Eight areas were selected from Setouchi region (annual precipitation,1 500-2000mm) and Pacific region (2500-4000mm).A pair of Japanese cedar and hinoki cypress forests was selected in each area. Leaves, roots, organic layer and surface soil at 5cm depth were collected at each forest and analyzed for δ15N. Relationship betweenδ15N pattern and soil processes was evaluated. δ15N in leaves and roots was not different between Setouchi and Pacific region whereasδ15N in surface soil was higher in Pacific region than in Setouchi region for both forest types. The enrichment factor from soil to leaves (δ15N leaf ~δ15N soil was lower in Pacific region than in Setouchi region. The enrichment factor was correlated with nitrification rate in surface soil positively and C/N ratio of decomposing leaves after 2 years negatively. The mechanism explaining this relationship was discussed.