The study aimed to investigate morphometric and meristic variability in the mud sleeper Butis koilomatodon (Bleeker, 1849) in the Mekong Delta. This species is a commercial fish species with a small-size and is mainly distributed in some coastal areas from Tra Vinh to Ca Mau provinces. In the present research, the parameters of morphomet and measurement, including the head length, body depth, eye diameter, distance of the two eyes, and the interrelationships among the morphometric variables, were determined. The results revealed that the total length and weight of the fish changed by sex. season, habitat, and the interaction between the seasons and habitats. Likewise, the meristic criteria were different between males and females, and the dry and wet seasons, but not by their interactions. The growth rate of males was faster than females. The outcomes also showed that the body size of this species was larger in the dry season and the largest fish were found in Duyen Hai and Tra Vinh provinces. The Findings would be useful not only for further effects of environmental factors on merphology but also for comparisons between congeners Butis morphologically