Onekotan (Russian Онекотан; jap温 祢 古 丹 岛, Onekotan -tō ) is an island belonging to Russia the northern Kurilengruppe. The closest islands are Makanruschi in the northwest and Charimkotan in the south.

It is of volcanic origin and forms a part of the fire ring, which stretches around the Pacific. Its area is 315 km ² (42 km in length and 8 to 17 km wide ).

Onekotan is remarkable by the two calderas in the south and north end of the island. In the south of the island is 1325 m high volcano Krenizyn rises from the Kolzewoje Lake ( Кольцевое / Ringsee ), which fills the Tao Rusyr caldera. In the north of the island is the 1019 m high volcano Nemo, also in a caldera, which is, however, only partially occupied by a lake ( Tschornoje Lake, Чёрное / Black Lake ).

Administratively, the island belongs to Rajon Severo- Kurilsk ( Nordkurilen, with the administrative center of Severo- Kurilsk on Paramushir ) of Sakhalin Oblast. Onekotan today is the largest uninhabited island of the Kuril Islands. By about 1994 was located on the east coast ( Mussel Bay, бухта Муссель ) a location of the Russian air defense, which is listed on Russian maps also under the name Onekotan. Before the 2nd World War, the island belonged to the Japanese sub-prefecture Nemuro.