Asiatic black bears (Ursus thibetanus) and sun bears (Helarctos malayanus) are sympatric in mainland Southeast Asia and face similar threats of habitat loss and commercial poaching. They are rarely seen but leave distinct signs, especially claw marks on climbed trees. These markings, which are potentially valuable indicators of presence, population status, and behavior of black bears and sun bears, have limited usefulness if the 2 species cannot be differentiated. We measured 121 claw mark imprints on climbed trees from 43 known (mainly captive) individual black bears and sun bears of both sexes in Thailand and Cambodia. The span across the markings made by 3, 4, or 5 claws from the hind foot was significantly greater for black bears than sun bears. We developed discriminant function models with these variables and arranged them in a 3-step process that distinguished claw marks as either sun bear, black bear, or indeterminate. This procedure correctly classified 95% of claw marks from the experimental animals. Tested on wild bears (at sites where only one species occurred), the procedure correctly classified 91% of claw marks of black bears in China (n = 94) and 100% of claw marks of sun bears in Indonesia (n = 32). The main limitation of the method was in distinguishing young, small black bears (cubs and yearlings) from sun bears. Nevertheless, application of these findings will be valuable in bear research and monitoring programs throughout Southeast Asia, where sign surveys have, until now, been hampered by the inability to differentiate these 2 ecologically and behaviorally similar species.