Buka Island is the second-largest island in the Autonomous Region of Bougainville, in eastern Papua New Guinea. It is in Buka Rural LLG of North Bougainville District, with the Autonomous Region's and district's capital city of Buka on the island.
The island is separated by the narrow Buka Passage from the northwestern coast of Bougainville Island, and has an area of approximately 500 km (190 sq mi). Buka, Bougainville Island and the Tabar Islands and their surrounding waters are identified as being part of the Solomon Archipelago terrestrial ecoregion and marine ecoregion.