Inner Sister Island, part of the Sister Islands Conservation Area, is a granite and dolerite island, with an area of 748 hectares (2.89 sq mi), located in Bass Strait, Tasmania, Australia.

The Inner Sister Island is located north of Flinders Island in the Furneaux Group. The island is grazed by sheep and annual muttonbirding takes place.

Seabirds and waders recorded as breeding on the island include little penguin, short-tailed shearwater, silver gull, Pacific gull, pied oystercatcher and sooty oystercatcher. Resident reptiles are the three-lined skink, White's skink, white-lipped snake and tiger snake. Apart from the sheep, mammals present on the island include the eastern barred bandicoot, Tasmanian pademelon and the introduced European hare.

• List of islands of Tasmania
• Outer Sister Island
• Shag Reef

• Harris, Stephen; Reid, Anthony, eds. (2010). Inner (West) Sister Island Scientific Expedition (PDF). Hobart: Department of Primary Industries, Parks, Water and Environment. ISBN 978-0-7246-6573-0. {{cite book}}: |work= ignored (help)