The moss floras of 9 small islands (less than 10 ha) in Lake Kamennoye (Kostomukshsky Strict Nature Reserve) were surveyed for the first time. Moss species lists (with 34 to 55 species) are given for each island. In total, 87 species of mosses were revealed, of which 11 species are new for the bryoflora of the nature reserve, 2 species are new for the moss flora of the Kuitozersko-Leksozersky floristic district. With the new findings, the moss flora of the Kostomukshsky Reserve comprises 159 species.