We bred black turtles (Chelonia agassizii) in captivity to improve our understanding of the reproductive biology of this species. One male and one female black turtle were maintained in a single outdoor tank with an openwater system at the Ocean Expo Park, Okinawa, Japan. Ultrasonographic observations indicated that the female (straight-line carapace length: 810 mm, body mass: 91.6 kg) first exhibited follicular development during March 2017. In May 2017, the male mounted the female for approximately 120 min, during which copulation occurred. The female later laid five clutches; the first eggs were released under water 32 days after mating, because of the absence of a suitable nesting substrate. After the female was transferred to another tank with an artificial beach, the second, third, and fifth clutches were laid on an artificial beach between July and August, but the fourth clutch was released underwater again. The mean (±standard deviation) internesting interval, clutch size, and egg diameter were 11.8±3.1 (range: 9–16) days, 45.2±13.8 (29–67) eggs, and 45.3±0.7 (44.0–47.0) mm, respectively. Hatchlings emerged from clutches 52–57 days after egg laying, with a total emergence success rate of 12.1% (14 hatchlings from 116 eggs). The straight-line carapace length and body mass of hatchlings were 48.8±2.0 (44.0–51.2) mm and 27.6±2.1 (24–30) g, respectively. This study is the first to report the breeding success of black turtles in captivity.