We investigated reproductive characteristics of brown bears (Ursus arctos yesoensis) in the Oshima Peninsula, Hokkaido, Japan, based on the study of individuals harvested from 1983 to 1987. Analyses were based on age-class and reproductive status data determined for 196 females killed during the study period. The minimum age at 1st parturition was 4 years, but frequency of reproductive success among females <6 years old was notably lower than that among females ≥6 years of age. Females <6 years old were more apt to produce single offspring and lose them during the 1st year. There appeared to be few changes in frequency of reproducing cubs among females 6–20 years of age. Females typically separated from young when young were 15–27 months old. For mature adult females, mean litter size was 1.8, and interval between births was 2.3–3.0 years. Embryo loss and neonatal mortality were uncommon.