In this study, the variation characteristics and revealed evolutionary selection mode at the molecular level of the major histocompatibility complex dra (mhc-dra) exon 2 in the six deer genera of family Cervidae were investigated and compared with cyt b gene. 246 bp of mhc-dra exon 2 sequences of six deer genera in family Cervidae were obtained based on sequencing method. The results showed that there were 18 polymorphic sites and 13 singleton variable sites. The nucleotide variations of mhc-dra exon 2 were low and each genus had its own unique variation loci. There were 20 putative antigen-binding sites in this region, in which position 63 and 18 were different from genus Equus and Homo, which suggested the six deer genera might have different antigen-binding model. According to the ratio of non-synonymous substitution rates (Ka) and synonymous substitution rates (Ks), the mhc-dra exon 2 is positive selection for Cervus, and is purifying selection for the other five genera. The Neighbor-joining method (NJ)，Maximum likelihood method (ML) and Bayesion inference (BI) of the mhc-dra exon 2 and cyt b were in a similar result, and all formed sister groups between the old world deer and the new one. The gene type of cyt b and mhc-dra exon 2 clearly showed subfamily Muntiacinae is a transition group between subfamily Cervinae and other subfamilies. Climate and environmental changes might

be potential reasons to promote the differentiation of mhc-dra exon 2.