Objective To investigate the sequence characteristic of black bear's mitochondrial NADH-ubiquinone oxidoreductase chain 4 gene(ND4).Methods Primers were designed according to certain species' NADH-ubiquinone oxidoreductase ND4 in which the DNA sequence had been reported.The DNA sequence was amplified by PCR from the Asian black bear Sichuan subspecies's(Ursus thibetanus mupinensis)hair-follicle tissue total DNA and were analyzed with its amino acid sequence.Results The ND4 gene sequence length was 1 402 bp and contained a 1 377-nucleotide open reading frame encoding 459 amino acid residues.The amino acid sequence's pI was 9.37 and weight was 51.5?10 3.The DNA sequence and corresponding amino acid sequence of black bear's ND4 gene had the high similarity with those of other mammalian animals' ND4 gene,and the similarity was 89% to 91% and 94% to 95%.The result of phylogenetic tree was basically consistent with the traditional species system phylogenetic relations.Topology prediction showed the Asian black bear Sichuan subspecies's ND4 proteins contained N-glycosylation site,kinase C phosphorylation sites,casein kinase Ⅱ phosphorylation site,N-myristoylation site and leucine-rich region.In addition,black bear's ND4 protein contained leucine zipper pattern and Leucine-rich region.Conclusion The mammalia animal's ND4 gene has the high conservative nature.The pretein coded by ND4 gene has high uniformity in the function.