In the forest ecosystems, soil arthropods (Arthropoda), as primary and secondary consumers, have a significant role in litter decay and decomposition processes. The abundance, diversity and community structure of arthropods in soil ecosystem; give rapid response to change of site characteristics. The current study was aimed to determine of seasonal variation of soil arthropods on forest floor at different altitudes in Uludag Fir (Abies nordmanniana subsp. bornmulleriana Mattf.) ecosystem which is an important forest tree species in Turkey. The study was conducted in pure fir stands at 1200-1600 m altitudes (4 elevation gradients) in Aladag, Bolu. The sampling was carried out for each winter, spring, summer and autumn seasons. The samples were collected from forest floor by pitfall traps. Variations of abundance and diversity of arthropods were evaluated according to seasons and altitudes. The distributions in trophic levels and biological diversity of arthropods were also determined. During the study, the maximum abundance of arthropods was 7576 individuals/m(2) in summer among seasons, and was 7854 individuals/m(2) at 1200 m altitude. Shannon-Wiener Index (H') and Species Richness (S') values were detected in the pitfall traps (H'=2.22; S'=22).