Kathleen Island is a steeply cliffed island, with an area of 11.35 ha and a height of 72 m, in south-eastern Australia. It is almost split by a deep gulch. It is part of the Breaksea 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.