Mutton Bird Island is an irregularly shaped island, with an area of 44 ha, in south-eastern Australia. Its highest point is 40 m asl. It is part of the Mutton Bird Island Group, lying close to the southern end of the south-western coast of Tasmania. It is also part of the Southwest National Park, and thus within the Tasmanian Wilderness World Heritage Site. The island is part of the Port Davey Islands Important Bird Area, so identified by BirdLife International because of its importance for breeding seabirds.