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Population characteristics of brown bears (Ursus arctos yesoensis) on Oshima Peninsula, Hokkaido, Japan were studied from January 1983 to May 1985. Although the sex ratio of bears greater than 2 years of age did not differ from 50:50, the younger age classes of males constituted a significantly (P < 0.05) larger portion of the kill than those of females. Within the study area, the age and sex structure of harvested bears did not differ by locality and did not change between the periods 1972-75 and 1981-84. There was no consistent trend in harvest from 1969 to 1984. Assuming the population was stationary, the average annual mortality rate was calculated from the age distribution of harvested bears as 20.5%, 14.2%, and 16.9% for males, females, and sexes combined, respectively. The differential vulnerability to hunting among the sexes may be 1 of the causes of these differing mortality rates.