Gastineau Channel is a channel between the mainland of the U.S. state of Alaska and Douglas Island in the Alexander Archipelago of southeastern Alaska. It separates Juneau on the mainland side from Douglas (now part of Juneau), on Douglas Island.

The channel is navigable by large ships only from the south east as far as the bridge connecting Douglas Island with the mainland. Between the bridge and the airport in Mendenhall Valley, the channel becomes navigable only to smaller craft and only at high tide.