Icefish (NeosaJanx sp) are high value species and have been popularly cultured large reservoirs in China. Icefish eggs had been introduced in Thac Ba reservoir in Yen Bai province from China since 1995. However, icefish appear in reservoir after 10 years. Taxonomy of this fish is difficult due to fish is small size, transparent color, white colored while dead fish. Application of molecular techniques in the classification of this species is necessary. 43 icefish samples were sequenced DNA cytochrome b gene region. BLAST analysis results showed that the DNA sequence of the fish samples collected from Thac Ba have the same level of species Ntangkahkeii, Ntaihuensis, Npseudotaihuensis from 99 to 100 percent. Phylogenetic trees showed icefishes were collected from Thac Ba reservoir are close relationship Ntangkahkeii, Ntaihuensis, Npseudotaihuensis (Fst = 0.003 to 0.006) and not close relationship N argentea, N anderssoni, N jordanni, N oligodontis, N reganius (Fst = 0.020 - 0.225). Ntangkahkeii, Ntaihuensis and Npseudotaihuensis are just a species because they are only different by 2 - 4 base. La tinh name of icefishes in Thac Ba reservoir is NeosaJanx tangkahkeii which first detected by Wu in 1931.