Lilla Karlsö is a small Swedish island in the Baltic Sea, situated about 3 km west of Gotland and 4.5 km from Stora Karlsö. It has an area of about 1.6 km² and is 66 meters high. Most of the island consists of a limestone plateau. Parts of the shoreline is bordered by steep cliffs. The island is mostly covered by alvar. There is also some very old broadleaf forest, which is unique for Gotland.