Mount Castner is a 5,535-foot (1,687 m) elevation glaciated summit located 44 mi (71 km) west of Valdez in the Chugach Mountains of the U.S. state of Alaska, on land managed by Chugach National Forest.

Although modest in elevation, relief is significant since the mountain rises from tidewater at Unakwik Inlet and College Fjord of Prince William Sound in approximately three miles.

The mountain's name was applied in 1910 by Lawrence Martin, and officially adopted by the United States Geological Survey.

This peak's name honors Joseph Compton Castner (1869–1946), who was with Captain Edwin F. Glenn during the exploration of this area in 1898.

[3] Weather systems coming off the Gulf of Alaska are forced upwards by the Chugach Mountains (orographic lift), causing heavy precipitation in the form of rainfall and snowfall.