<p>Urbanization is widely recognized as a major driver of global biodiversity decline; however, urban greenspaces, particularly extensive and well-connected natural habitat patches, hold considerable potential for biodiversity conservation. Coastal forests, characterized by their linear and contiguous distribution along sand dunes, may play an important role in maintaining biodiversity within urban coastal landscapes. Despite their ecological importance, limited information is available regarding how urbanization and local habitat conditions jointly influence ground-dwelling spider communities in these ecosystems. In this study, we examined the effects of local- and landscape-level factors on the diversity and functional traits of ground-dwelling spider assemblages in coastal forests in Niigata, Japan. Spiders were sampled along an urbanization gradient, and local environmental characteristics were quantified to assess their influence on spider communities. Urbanization intensity was associated with lower spider species richness and abundance, suggesting that urbanization in the surrounding landscape may diminish the capacity of coastal forests to support diverse ground-active spider assemblages. At the local scale, canopy openness was positively associated with spider species richness, whereas ground-layer vegetation cover was positively associated with spider abundance. Urbanization intensity, canopy openness, and leaf litter mass also influenced assemblage composition, with assemblages in highly urbanized landscapes and closed forests characterized by smaller-bodied species. These findings indicate that both surrounding urbanization and within-forest environmental conditions shape ground-active spider assemblages in coastal forests. Conservation and management of coastal urban forests should therefore consider both connectivity with surrounding habitat patches and the maintenance of heterogeneous forest-floor conditions.</p>