The deposits of Biśnik Cave yielded numerous bear remains from sediments dated to the MIS 8–MIS 3 interval. This situation allowed examination of the paleoecology of Ursus spelaeus over time, compared with two other species of bears: Ursus deningeri and Ursus arctos, also present in fossil material from Biśnik Cave. The stable isotope ratios (δ13C, δ18O) in tooth enamel were applied in combination with examination of seasonal deposition of dental cementum. The δ13C values showed the diet of each bear species stayed in the range of C 3 plants. Results for U. spelaeus showed a wider range of δ13C values than for U. deningeri or U. arctos. The values are relatively negative in comparison to fossil bears from other European sites. Low δ13C values observed in bears from Biśnik Cave could be linked to a canopy effect and document a forested environment for these bears. No correlation between δ18O and δ13C values was noted. The cementum analysis revealed that season of death of all species was winter and all studied specimens died during hibernation. The highest mortality concerned mostly individuals below 4 years old and the highest individual aged was U. deningeri.