To describe the life history of an endangered insular subtropical subspecies of the Common Buzzard Buteo buteo toyoshimai, we studied its breeding biology on Chichijima, Ogasawara Islands in the Pacific Ocean. Several nests were found in single territories, most of them located on cliffs. Social behavior reached peaks in winter, during December and February. Copulation between paired mates occurred from January to June. Egg laying was estimated to begin in late January, and lasted a minimum of two months. Incubation ranged from 30 to 33 days and the nestling period from 33 to 45 days. Both females and males incubated the eggs, but only females brooded the nestlings. Both sexes brought prey to the nest; however, only females fed prey directly to their young nestlings. Within two weeks of hatching, the time spent by females at the nest decreased to less than 50% of the observation time. The means of clutch, early brood (1–3 weeks), late brood (>4 weeks), and fledgling sizes were 2.2, 1.8, 1.3, and 1.2, respectively. Brood reduction occurred in nests containing several nestlings. Some fledglings depended on their parents for several months, staying in their parents' territories until October. The breeding success rate in terms of the proportion of pairs with fledglings was 0.35. These results suggest that the sub-tropical Ogasawara race of the Common Buzzard is socially monogamous and has a distinct breeding season.