Dispersion structure with reference to topography was analyzed by Iδ-method in the natural populations of Japanese red pine (Pinus densiflora S[IEB]. & Zucc.). Most of stands less than 10 years old on the bank-slopes along a sunny road exhibited the aggregated distribution , regardless of the inclination and the direction of slopes. This contagiousness was seemed to closely relate with micro-topography of the stands and behavior of seeds with wings after landing onto the ground. All the stands more than 10 years old denoted even-spacing. The change of pattern from the aggregated distribution to the uniform suggested that mortality process operates density-dependently in local among trees. From the standpoint of dispersion structure , there was suggested a possibility of predicting the exact time when self-thinning would start.