Izu Ōshima is an inhabited volcanic island in the Izu archipelago, part of the Tokyo region of Japan. It lies off the coast of Honshu, bordering Sagami Bay and the Pacific Ocean, about 22 km (14 mi) east of the Izu Peninsula and 36 km (22 mi) southwest of the Bōsō Peninsula.
At 91.06 km2 (35.16 sq mi), Izu Ōshima is the largest and closest of Tokyo's outlying islands, a group that also includes the Ogasawara Islands. Like the other islands in the Izu group, it forms part of the Fuji-Hakone-Izu National Park.