Louisa Island is an irregularly shaped 23 ha island in south-eastern Australia. It is part of the Maatsuyker Island Group, lying close to the southern end of the south-western coast of Tasmania. Its highest point is 80 m asl and, at low tide, it is joined to the mainland by a 250 m sand spit. It is part of the Southwest National Park, and thus within the Tasmanian Wilderness World Heritage Site. The island is part of the Maatsuyker Island Group Important Bird Area, identified as such by BirdLife International because of its importance as a breeding site for seabirds.