We compared the structure of spider assemblages between the upper and lower canopy layers, and between the canopy and forest floor, in plantations of evergreen cedar (Cryptomeria japonica) and deciduous larch (Larix kaempferi). The estimated number of species was similar between the upper and lower canopy layers (49.0 vs 45.1) in C. japonica, but was noticeably smaller in the upper canopy layer (11.3) than in the lower layer (36.9) in L. kaempferi. Arboreal spider assemblages in the canopy differed significantly between the upper and lower layers in both C. japonica and L. kaempferi stands, based on an abundance-based measure. However, based on an incidence-based measure, they only differed significantly between layers in the L. kaempferi stand. The spider assemblages also differed distinctly between the canopy and the forest floor in both stands. Wandering spiders and orb-web builders were dominant in the canopy, while space-web builders dominated the forest floor in the C. japonica stand. In the L. kaempferi stand, wandering spiders dominated both the canopy and the forest floor. Our results suggested that spider assemblages in conifer plantations were distinctive among strata because of differences in such factors as resource quality (i.e., living or dead foliage) and association with adjacent layers along the vertical gradient of the forests.