South West Mutton Bird Islet is a dome-shaped islet, with an area of 0.52 ha, in south-eastern Australia. Its highest point is 28 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.