volcanic island, North Kyŏngsang do (province), South Korea. It lies in the East Sea (Sea of Japan), 75 miles (120 km) off the northeastern coast of South Korea, and has an area of 28 square miles (73 square km). Before its domination by the Silla kingdom (57 BC–AD 935) in 512, it was an independent kingdom named Usan-guk. The island's summit, Sŏngin Peak (3,228 feet 【984 metres】), has a caldera crater.

The entire coastline has rocky bluffs 100–300 feet (30–90 metres) high, which preclude port development. Neighbouring waters with the interchange of warm and cold currents offer good fishing ground for cuttlefish, which is exported, and various other marine products. Agricultural products, however, must be imported. The mountain area produces Chinese juniper, birch, and princess trees, all used to make quality furniture. Ullŭng Island is connected with the mainland by regular sea routes.