Swainson Island is an island, with an adjacent islet, with a combined area of 4.14 ha, in south-western Tasmania. It is part of the Swainson Island Group, lying close to the southern end of the 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.