| Siluriformes belonging to Ostariophysi, Teleostei, is a group of fishes that are mainly lived in freshwater and broadly distributed in all continents. The phylogenetic relationships of the species, genera and families in this order are not fully identified. The mitochondrial DMA cytochrome b gene was sequenced from 32 siluriforms which are belonging to 22 genera and 10 families. Aligned with cytochrome b sequences from 29 siluriforms in Japan, Korea, Russia, Africa, North America and South America retrieved from GenBank, and selected Astyanax mexicanus, Phenacogrammus interruptus, Cyprinus carpio and Oncorhynchus mykiss as outgroups, which are belonging to Characiformes, Cypriniformes and Salmoniformes, respectively. We constructed a matrix of 65 DMA sequences. The Kimura's two-parameter distances were calculated and molecular phylogenetic trees were constructed by using the maximum parsimony (MP), maximum likelihood (ML) and neighbor-joining (NJ) methods. The results show that (1) there exist 3-bp deletions of mitochondria! cytochrome b gene compared with characiforms, cypriniforms and salmoniforms; (2)the molecular phylogenetic trees suggest that siluriforms form a monophyletic group and have a close relationship with characiforms; (3) the families of Pangasiidae, Claroteidae, Ictaluridae, Cranoglanididae, Schilbidae and Clariidae form a monophyletic group in the three molecular phylogenetic trees. The family Bagridae branched with Schilbidae which comes from China; the family Akysidae branched with Amblycipitidae, but the phylogenetic positions of the families Siluridae, Sisoridae and Pimelodidae are not recognised. (4) the molecular phylogenetic trees suggest that bagrid catfishes form a monophyletic group, and the genus Mystus is the earliest divergent in East Asian bagrid catfishes, as well as the genus Pseudobagrus is a monophyletic group but the genus Pelteobagrus and Leiocassis are complicated.
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