Trematoda fauna of fish in Lake Ladoga includes 46 species. The trematoda specifity exists a mixed character as it is observed for Baltic province totally. There are 3 main trematoda complexes in Lake Ladoga: boreal flatland, arctic freshwater, boreal piedmont. The trematode species diversity depends on the lake location on the boarders of Circumpolar and Mediterranean sub areas. The Cyprinidae fish take the most part in trematode diversity and quantity.