The relatively population density and ratio of adult to young of the Black Bear (Ursus thibetanus) and the Brown Bear (U.arctos) were surveyed on transects in broad-leaved pine mixed forest (40 000 hm²) and conifer forest (30 000 hm²) in Changbai Mountain Nature Reserve from 1986 to 2010.Total of 65 Black Bear (2.6 ind/a) and 46 Brown Bear (1.8 ind/a) were accumulatively counted. Both the population size of Black and Brown Bear varied greatly with a trend of decline. The current relative density of Black Bear had decreased 93.4% and the percentage of young to population had decline from 17.2% to zero since 1980s. The relative density of Brown Bear was very low (0.021-0.029 ind/km), and the ratio of young to adult was only 7.1%. The lower percentage of young bears found in this survey indicated that both bear species were endangered in the study area. Habitat reduction and fragmentation, poaching are considered as major reason for population declined in the Changbai Mountain Natural Reserve.