In forest, trees enhance the soil reinforcement (SR) with their roots and contribute to slope stability. It is known that the SR increases with the number and diameter of roots. Thus SR is expected to decrease significantly near the center of horizontal distance between trees, where the number and diameter of roots decrease. Previous studies for SR have been conducted in mostly single-species plantations and a few studies in secondary forests. Since Japan has large area of secondary forests, we need to reveal the effect of mixed tree species on SR. Therefore, the purpose of this study is evaluation of slope stability at the center of gaps in a secondary forest composed of different species. The study site locates in Mt. Rokko in Hyogo Prefecture. The excavation surveys for calculation SR were conducted in December 2020 at the center between mature Pinus densiflora and Eurya japonica trees. As the results, the SR values in secondary forest was comparable to those reported in previous studies conducted in mature conifer plantation, and they had greater variation among plots than plantation. When comparing the SR between tree species P. densiflora, the canopy species had higher value than E. japonica, the understory species.