Brachyuran crabs are crustacean groups with high species diversity, widely distribute and play an important ecological role in the mangrove forest area. In this study, samples of the brachyuran crabs were collected at 12 sampling sites in the mangrove forest and mudflat habitat in the mangrove forest area in Cu Lao Dung district, Soc Trang province in April (dry season) and September (rainy season) in 2019. There were 34 species belonging to 17 genera and 7 families, recorded in the mangrove forest area. The Ocypodidae family were recorded with the highest number of species of 11 species, following by Sesarmidae family (7 species), Portunidae family (6 species), Varunidae family (4 species), Grapsidae family (3 species), Matutidae family (2 species), and Xanthidae family (1 species). The species diversity and population density of brachyuran crabs in mangrove forest habitat (with 26 species and the population density ranged from 34.0±8.4 to 53.8±15.4 (inds/m²)) were higher than in the mudflat habitat (with 15 species and the population density ranged from 12.4±1.9 to 13.6±3.6 (inds/m²)). The species diversity and population density of brachyuran crabs in the rainy season (with 28 species and the population density ranged from 13.6±3.6 to 53.8±8.4 (inds/m²)) were higher than in the dry season (with 14 species and the population density ranged from 12.4±1.9 to 34.0±8.4 (inds/m²)).