The body size is one of the main attributes of living organisms. The knowledge of body size patterns of co-occurring species and the related factors can contribute to the understanding of many ecological processes. The aim of the study was the analysis of the distribution of the spider species of different size in heterogeneous forest habitats: ground, herbaceous vegetation, tree trunks and leaves. The research was conducted in deciduous stands of the Białowieża Forest (eastern Poland). Spiders were collected by: a) pitfall traps and sieving the litter through an entomological sieve for the ground layer; b) sweep-netting for herbaceous vegetation; c) bark traps for tree trunks and d) shaking the branches of trees and shrubs for leaves. In total, 247 spider species belonging to 22 families were recorded: 195 species in the ground layer, 122 in herbaceous vegetation, 60 on trunks, and 48 on leaves. The analysis revealed that ground layer was inhabited by the small sized species (mean 5.2 ± 0.11 mm) while larger species inhabited herbaceous vegetation (mean 6.6 ± 0.26 mm), trunks (7.2 ± 0.20 mm) and leaves (6.8 ± 0.41 mm). Moreover, the mean species body size decreased with the increasing number of collected species. Several potential mechanisms are discussed as those determining the preference of various sized spider species in particular habitats like different microclimatic conditions, the nutritional quality of prey and predation. Moreover, the very likely reason of differences in the size of spider species between the ground layer and other habitats is the most complex structure of the former habitat.