Kupreanof Island is an island in the Alexander Archipelago in southeastern Alaska at 56°48' N 133°25' W. The island is 84 km (52 miles) long and 32 km (20 miles). The Lindenberg Peninsula, on the southeast side of the island is considered part of the island. The peninsula is separated from the rest of the island by the a narrow strait called the Duncan Canal.

The island is named after Baron Ivan Antonovich Kupreianov, a head of the Russian-American Company.

The largest settlement on the island is Kake.