Kunashir Island (国後島:Kunashiri in Japanese, Кунашир (Kunashir) in Russian, Black Island in Ainu language), a southwestern island of the Kuril Islands, located in the Sakhalin Oblast of the Russian Federation. Although this island is a part of Russia, Japan maintains a claim to it along with the other three islands (see Kuril Island conflict).

It lies between the straits of Kunashir, Catherine, Izmena and South Kuril.

• Area - 1550 sq km
• Length - 123 km
• Width - 4-30 km

There is a chain of volcanoes along the island with some of them still active (Tyatya (1819 m), Rurui in the Dokuchaev ridge, Mendeleev and Golovnin).

The island is formed with the volcanic and crystalline rocks. It has many hot springs. The climate is of monsoon type. The vegetation mostly consists of spruce, pine, fir, and mixed deciduous forests with lianas and Kuril bamboo underbrush. The mountains are covered with birch and Siberian Dwarf Pine scrub, herbaceous flowers or bare rocks.

Primary economic activity is fishery and fishing industry. The island has a port next to the town of Yuzhno-Kurilsk.