Abstract: The aim of this study was to elucidate the species diversity of larva trematodes in the Mazandaran Province, Northern Iran. In this cross-sectional study, a total of 3,266 lymnaeid snails from 3 species were collected from different parts of streams, swamps, rice fields and rivers in the central areas of Mazandaran Province (Sari, Neka, Qaemshahr and Savad-Koh cities), during April to September, 2008. The samples were tested by crushing and emerging methods. From the total of examined snails, 119 (3.6%) were found to be infected with the lymnaeid snails. Lymnaea gedrosiana were found to be infected with the Furcocercariae of Diplostomidae, Clinostomidae, Echinostomatidae and also cercariae of the Plagiorchiidae. The latest infection was found to be in L. palustris. The Mazandaran Province with its temperate climate is a suitable place for living of snails, particularly lymnaeidae, that could have a significant role as an intermediate host of diseases.