Brunei is on the island of Borneo.
Borneo ( [ ˈbɔrnioʊ ] Pulau Borneo , Kalimantan ) is the third-largest island in the world and the second-largest island in Asia . Brunei . Brunei is the only sovereign state completely on the island of Borneo ; the remainder of the island 's territory is divided between the nations of Malaysia and Indonesia . At the peak of the Bruneian Empire , Sultan Bolkiah ( reigned 1485 -- 1528 ) is alleged to have had control over most regions of Borneo , including modern-day Sarawak and Sabah , as well as the Sulu archipelago off the northeast tip of Borneo , Seludong ( modern-day Manila ) , and the islands off the northwest tip of Borneo .