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Earthworm population, as a biotic factor, affects health and productivity of forest ecosystems. Earthworm density and biomass indicates biological activities and quality of soils. In order to get the benefit of earthworm ecological potential in Zagros forest management, the current biological activities as well as environmental factors impacting of this invertebrate have to be understood. This study aims at determining the density and biomass of earthworm and investigating their relationships to environmental factors including seasonal variability, soil depth and the tree canopy in Brant’s oak (Quercus brantii Lindl.) high forest of Darber area (Khoram Abad, Lorestan). Thirty two single-stem trees of Brant’s oak were sampled. Earthworm’s density and biomass were measured in spring and autumn, under and away from the canopy, using soil profile. Soil profiles were 50 cm deep and samples were taken from layers at 0-10, 10-30, and 30-50 cm depth. Means of earthworm’s density and biomass were compared using one way ANOVA and independent t-test at the 95% probability level. The results of this study showed that seasonal variation, soil layers depth and tree canopy had significant impacts on earthworm’s density and biomass. Earthworm’s density and biomass were decreased in autumn and also in spots away from tree canopy. Minimizing topsoil disturbance and expanding canopy coverage in managing Zagros forest resources could optimize the environmental conditions for earthworm biological activity, which would improve soil quality and ecosystem health.