Abstract：In order to study Tibetan sheep (Ovis aries) DRB3 gene polymorphism, determine its allele number, nucleotide polymorphism sites, analysis the genetic relationship and evolutionary significance of the alleles. Variation in the 500 Tibetan sheep DRB3 gene was investigated by PCR-SSCP method, followed by cloning and DNA sequencing. The results showed that there were 37 alleles were identified. There were 82 nucleotide polymorphism sites were identified in 37 sheep DRB3 gene haplotypes. Thirty five novel DRB3 exon 2 alleles were found comparison with GenBank sequences. The phylogenetic tree results showed that the 37 haplotypes of Tibetan sheep DRB3 gene exon 2 can divide into two clusters. It is showed that Tibetan sheep DRB3 gene exon 2 has high level of sequence polymorphism，Tibetan sheep DRB3 gene was differentiated into two major categories alleles from two mutant alleles at first.
