Spiders are among the most important predators in forest litter layer that control food chain and decomposition process. However, little is known about the changes in litter-spider communities from wind-exposed to wind-shielded areas during monsoon seasons, and their roles in litter arthropod distribution and decomposition processes. In the present study, the densities and diversities of the spider communities in litter were examined at the two locations in monsoon and non-monsoon seasons in southern Taiwan. Enclosures with/without the spider Ctenus yaeyamensi were set up to compare litter arthropod distribution and decomposition rates in litterbags in different sampling units. It was found that the mean density of litter spiders was significantly greater in wind-shielded area than wind-exposed area. There was a marked impact of structure and depth of litter layers on guild composition, but not on the diversity indices of the litter spider communities. The litter invertebrates and decomposition rates did not differ between enclosures with/without spiders. However, there was a marked difference in litter arthropod abundance between monsoon and non-monsoon seasons in wind-exposed areas. The decomposition rate was remarkably greater in non-monsoon seasons than in monsoon seasons, whereas there were no marked differences between wind-shielded and wind-exposed locations. It was concluded that litter arthropod distribution and related decomposition were affected by variation of monsoon seasons but not by spider presence/absence in Nanjenshan Rain Forest.