Kolchak Island is an island in the Kara Sea located NE of the Shturmanov Peninsula, in an area of skerries south of the Nordenskiöld Archipelago. This island is named after Alexander Kolchak, its discoverer and explorer. He had joined Eduard Toll's 1900 arctic expedition, which explored many little-known islands of the Kara Sea.

Kolchak Island was first depicted on a map in 1901 and, compared to other large islands in the area, it has a quite regular shape. Its length is 21 km and its maximum width 6.5 km. It is covered with tundra vegetation in the summer, but most of the year it lies under a shroud of snow.

This island is located 40 km from the western end of the Taymyr Gulf and only 14 km southeast of Taymyr Island. It separated from the nearest coast by a narrow sound that is about one km in width in its narrowest stretch.

The climate in the area is severe, with long and bitter winters and frequent blizzards and gales. The sea surrounding Kolchak Island is covered with pack ice in the winter and there are numerous ice floes even in the summer, so that most of the year it is merged with the mainland.

Kolchak Island belongs to the Krasnoyarsk Krai administrative division of the Russian Federation and is part of the Great Arctic State Nature Reserve, the largest nature reserve of Russia.