We investigated the denning ecology of 19 (12 males and 7 females) radiocollared Asiatic black bears (Ursus thibetanus) from 2001 to 2004 in the Misaka Mountains, central Japan. We approached 14 dens of 5 females on foot. Thirteen dens were located in cavities that formed between the roots of trees growing on the upper edges of landslides or steep inclines, and 1 den was located in a cavity under a rocky ledge. We were unable to access 39 more dens for which we had approximate locations due to a combination of distance from roads, steep terrain, and high shrub densities. All 53 dens we approached or approximately located were on steep slopes. There were few large trees with large cavities in the study area, which may explain why we failed to find any dens in such cavities.