Abstract: The major expressed MHC class I and beta 2-microglobulin (β2m) genes were cloned from a silky chicken breed and Numida Meleagris breed (the MHC class I genes were designated BF2*SI and BF2*NM , respectively ). The allelic polymorphisms in the population of the two chicken breeds were investigated. The amino acids homologies among BF2*SI, BF2*NM alleles were 75.5%～93.9% and 81.1%～98.5%, respectively. Compared with human HLAA2, seven of key amino acids of the peptide binding sites were conserved in BF2*SI, but six in BF2*NM. Twenty-four high amino acids substitution sites (amino acids substitutions ratio≥4.0) were found in the peptide-binding domain (PBD) of BF2*SI , and two sites (position 69 and 9) displayed the amino acids substitutions ratio≥8.0. Unlike BF2*SI, only six high amino acids substitution sites were found in the PBD of BF2*NM. The numbers of high amino acids substitution sites in PBD of Leghorn chicken BF2 was lower than that of BF2*SI, but higher than that of BF2*NM. According to homology ratios, α1, α2, α3 of BF2*SI were classed into 4, 3 and 3 types, and α1, α2, α3 of BF2*NM were classed into 3, 3 and 1 types, respectively. Six BF2*SI genes were subdivided to 5 lineages (A, B, C, D and E), whereas five BF2*NM genes were subdivided to 3 lineages (A, B, C). Comparison the amino acids homology ratios of α1, α2 domains in BF2*SI, BF2*NM with that in BF2* 21 with resistance to MDV revealed that BF2*03SI, BF2*04SI, BF2*05NM were most similar to BF2* 21 in α1 domains (with homology ratios of 86.4%, 86.4%, 87.5%, respectively), and BF2*05SI, BF2*05NM were most similar to BF2* 21 in α2 domains (with homology ratios of both 93.4%). The β2m genes of silky chicken breed and Numida Meleagris breed could be classed into 2 types (type 1,type 2) based on the amino acids sequences of mature peptides. The type 1 was identical to the β 2m genes of Leghorn chicken(accession number M84767) , but type 2 only had the homology ratio of 87.5% with type 1. The results suggested that the BF2 and β2m genes of each chicken breed own its special molecular characters.