Buckle Island is one of the three main islands in the uninhabited Balleny Islands group located in the Southern Ocean. It lies 25 kilometres northwest of Sturge Island and eight kilometres southeast of Young Island, some 110 kilometres north-northeast of Belousov Point on the Antarctic mainland.

The island is roughly triangular in shape, with long east and west coasts and a short north coast. It is approximately four kilometres in width at the north, and its maximum length is eight kilometres. The island is of volcanic origin, and is still volcanically active, the last eruption being in 1899.

The northernmost point of Buckle Island is Cape Cornish. Several small islets also lie in the channel separating Cape Cornish and Young Island, the largest of which is Borradaile Island. Several small islets lie off the island's southern extremity, Cape McNab, including Sabrina Islet and the 80 metre tall stack of The Monolith. Both Buckle Island and Sabrina Islet are home to colonies of Adelie and Chinstrap penguins.

The island forms part of the Ross Dependency, claimed by New Zealand (see claims on Antarctica).