Kuiu Island is an island in the Alexander Archipelago in southeastern Alaska. It lies between Kupreanof Island, to its east, and Baranof Island, to its west. The island is 105 km long, and 10 to 23 km wide. It is nearly cut in two by Affleck Canal. The Kuiu Wilderness and Tebenkof Bay Wilderness are federally designated wilderness areas within the Tongass National Forest, located on Kuiu Island, Petersburg Census Area, Alaska.
Kuiu Island is deeply dissected by fiords that nearly divide the island into narrow land bridges in several places. The resulting bottlenecks pose obstacles to wildlife movements. The Bay of Pillars-to-Port Camden portage was one of four areas in Southeast identified in the Forest Plan as problematic for wildlife dispersal, and remains a priority for maintaining connectivity of high value habitats.