The present study was performed to investigate Gastropods diversity in mangrove forests located at Chabahar Township, Sistan & Baluchestan, Iran. For this purpose some homogenous forest masses were isolated and field visits were done. In each mass, three vertical transects were selected at the site of water contact up to land contact and sediment sampling was conducted from first (in contact with the water), middle, and end points of each transect. Three samples were collected in triplicates and during four successive seasons. Of 2119 collected gastropod samples, 44 species were identified from 35 genera and 22 families, among which three species were identified up to family level, nine up to genus level, and the remaining up to species level. Among the species identified, Asseminea sp.2 and Asseminea sp.1 were the most abundant species with 41.49% and 30.77%, respectively. Species Cerithidea cingulata (11.04%)and Stenothyra arabica (6.09%) were in subsequent rankings. The identified gastropods at the first point belonged to 13 families, 16 genera, and 17 species, among which five species were observed only in this area: Cerithiopsis sp., Melampus castaneus, Haminoea cf vitra, Nassarius sp. and Umbonium vestiarium. The gastropods had the highest species number at middle point belonging to 20 families, 28 genera, and 36 species and the number of 22 species (the highest species number) was observed only in this region. Except two species Cerithium sp.andFinella pupoides, other gastropod species of end point were also present in other regions. Gastropods of this region belonged to 7 families, 10 genera, and 12 species. Comparing this results with other mangrove forests shows that from the east to west the gastropods diversity has reducing trend; and the studied area is the most diverse region in Iran. This study recorded 13 new species from Iran that wasn’t reported before.