Lilla Karlsö is a small Swedish island in the Baltic Sea, situated about west of Gotland and from Stora Karlsö. It has an area of about and is 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. There are several caves and up to high limestone pillars.