To elucidate the composition and characteristics of fish fauna in the Mengjiang River (located in the Pearl River system), Guizhou, the fish species from the river was thoroughly surveyed as well as the fish specimen collected by gill-net from 20 sampling sites along the Mengjiang River between April 2014 to September 2015 (Fig. 1). A total of 5206 individuals of fish specimen belonging to 65 species or sub-species from the Mengjiang River were collected in this research. Combining with historical records, totally 75 species or sub-species of fishes , which belonged to 7 orders, 18 families and 56 genera, distributed in the Mengjiang river (Appendix). Of these fishes, Anguilla japonica was migratory species, Gambusia affinis, Neosalanx tangkahkeii and Oreochromis niloticus were introduced ones, and 41 species or sub-species were new records in the Mengjiang River. Total of 51 species or sub-species fishes belonged to Cypriniformes that constituted the largest fish group and took up 68.0% of fishes in the river. The cyprinid fishes were dominant group and accounted for 60.0% of total fish species in the Mengjiang River. Then 3 or 4 species respectively belonged to each family of Siluridae, Bagridae in Siluriformes. The fish fauna in the Mengjiang River was much similar to that in the Beipan River according to the UPGMA clustering analysis (Fig. 2). The fish fauna of the river was mainly composed of fish representative species in South China region and then East China region. No fish species which occur in North China region was detected by this study. The cyprinid fishes in the Mengjiang River comprised the species in “Early Tertiary Period Primitive Group”, “East Asia Group”, “South Group” and “Qinghai-Tibetan plateau group” and excluded the fishes in “North Cold Water Group”, and the “Early Tertiary Period Primitive Group” had much more fish species than any of the other groups in Cyprinidae in the river. The fish fauna in the Mengjiang River showed high species diversity and included complicate ichthyofauna components. Also, it comprised abundant fish species that are threatened and endemic to China, as well as fishes living in riptide. Moreover, the fish fauna was characterized by the fish species group only occurring in the East Yunnan-Guizhou Plateau. The fish fauna in the Mengjiang River belonged to the South Asiatic Subregion in the Oriental Region.