Abstract: The diversity of the crabs in the Pichavaram mangroves for the first time has shown that there are 46 species of crabs from the five different stations. The neritic zone (Chinnavaikal) was rich in species composition (35 species). The freshwater zone was poor in species composition (14 species) and population density. Among the crab species Sesarma and Uca species were dominant in almost all the stations. Grapsid crabs were the most dominant species. Neritic and Avicennia zones showed more number of crab species but less number of species was noted in slightly saline zone. The substrate suitability, tidal inundations mangroves distribution and salinity were the possible factors for distribution of crabs in Pichavaram mangroves.