The area of secondary forests in Japan accounts for 24% of the total forest area. Since land uses in secondary forests have changed, secondary forests have been recovering and, according to the succession, evergreen tree species are expected to increase gradually. The succession process in secondary forests is also influenced by recently occurred natural disturbances. Seedling is a vital stage for tree regeneration, and biotic and abiotic factors impact tree species establishment through linking with functional traits. However, few studies have paid attention to evaluating the regeneration process by monitoring tree seedling communities, environmental conditions, and functional traits in secondary forests. In this study, we conducted a long-term tree seedling census（2009-2014 and 2018-2020) and measured environmental factors including canopy openness, soil water content, soil nutrients, litterfall and slope, and tree seedling traits for 13 species (SLA, leaf thickness, SRL, LDMC, leaf nitrogen concentration) in the Kaisho warm temperate secondary forest to understand the changes in the seedling community and forest environments. Our results indicate that the responses of current-year seedlings to environmental conditions such as canopy openness, soil water content, soil nutrients could be explained by the functional traits.