Negative density-dependent effects of closely related species have been reported in some tropical rainforest trees. However, its generality is still controversial. This study aimed to understand the effects of environment and phylogenetic neighborhood on seedling mortality in a tropical rainforest in Borneo. The seedling data of 17,436 individuals of 526 species were collected at 1,255 2 x 2 m²-plots in 2000 and 2009. Topography, soil properties, and canopy height were also measured at each plot for environment data. We analyzed the effects of environment and conspecific density on seedling mortality using community-wide GLMM and species-specific slope GLMM. The results showed that initial seedling height, habitat, and conspecific seedling density were significantly related to seedling mortality. Taller seedlings showed lower mortality, seedlings on steep slopes with intermediate soil fertility showed higher mortality, and higher conspecific seedling density was associated with higher mortality. The species-specific slope model was better than the community-wide model, indicating that the effects of variables differed among species. The presentation will show whether the species-specific effects are phylogenetically conservative, i.e., whether closely related species respond similarly.