Diversity of fauna in mangrove forest of Sri lanka is so immense but is a relatively poorly dealt subject. The studies dealt with mangrove crabs is Sri lanka are restricted to the study carried out by De Silva 1985 on fauna in five mangrove forest of Sri lanka and the study done by pinto 1984 on the crabs of negombo estuary. It was the felt that it important to recognize the diversity of crabs in mangrove forest of Sri Lanka before initiating studies on their role in the mangrove forest . The present study was carried out to investigate the diversity and environmental interactions of mangrove crabs in the Kadolkele mangrove ecosystem, in the Negonbo estuary. The distribution of crabs in different zone of mangrove was also investigated.