The study was conducted based on the analysis of specimens collected in the coastal sea of Nghi Son Town, Thanh Hoa Province, from December 2019 to December 2020. The results identified three species in the genus Upeneus (Mullidae): Upeneus tragula Richardson, 1846, Upeneus sulphureus Cuvier, 1829, and Upeneus japonicus Houttuyn, 1782. The study also analysed the differences of above specimens in comparison with the previous studies of FAO (2001) [1], Nguyen et al. (2007) [6], although there are some differences in the ratios of the body part with the standard length (Lo) and head length (T) but insignificant. Analysis of the morphological characteristics of the three species also showed that the differentiation was most clearly expressed in the number spines of the first dorsal fin, the soft rays of pectoral fin, lateral scales, colour and pattern on the body; the combination of these features can be used as a standard for classifying species, among them the differences in color and pattern are important classification characteristics.