In the rivers of the western and central parts of the Roztocze Upland, SE Poland, 37 species of Mollusca were found: 23 Gastropoda and 14 Bivalvia In the upper course of the Wieprz River 34 species of Mollusca occurred. In the Tanew River and its tributaries 24 species were found. In all investigated rivers bivalves of the genus Pisidium and the snail Ancylus fluviatilis predominated.