Kupreanof Island is an island in the Alexander Archipelago in southeastern Alaska at . The island is 84 km (52 miles) long and 32 km (20 miles) wide with a total land area is 2,802.84 km² (1,082.18 square miles), making it the 13th largest island in the United States and the 170th largest island in the world. 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's population was 785 at the 2000 census.
The largest settlement on the island is Kake, on the northwestern side of the island. The only other city is Kupreanof, on the eastern side, across the Wrangell Narrows from the city of Petersburg on nearby Mitkof Island.