The study was aimed to determine the species diversity, carapace width (CW)-body weight (BW) relationship, size distribution and sex ratio of mud crab, genus scylla from Setiu Wetlands of Terengganu coastal waters, Malaysia. A total of 1,000 crabs of various sizes (6 -15 em CW), sex and species were randomly collected during the monsoon season. The study showed that the mud crab species composition was dominated by Scylla olivacea (65.0%), followed by Scylla paramamosain (21.8%) and Scylla tranquebarica (13.2%). The male crabs were significantly bigger and heavier than females for all the mud crab species sampled. The rate of increase in body weight of S. olivacea was more than the other two mud crab species of S. paramamosain and S. tranquebarica. The dominant size range with respect to carapace width for all the mud crabs sampled was between 9.Ocm and 9.9cm. The male crabs are relatively more abundant than the females for all the mud crab species sampled (1 :0.82).