Abstract: A 374bp fragment spanning over exon 2 of major histocompatibility complex B-LBⅡ gene was amplified, cloned and sequenced in eight Chinese indigenous chicken breeds and one introduced breed. Twenty new B-LBⅡalleles were found in the chicken breeds sampled. The polymorphism of the exon 2 was investigated by PCR-RFLP technique at the six loci of AluⅠ, CaiⅠ, CfrⅠ, Hin1Ⅰ,HinfⅠand RsaⅠ. The observed homozygous genotypes at the six loci were utilized to tentatively identify the alleles of B-LBⅡ genes in the animals analyzed. It indicated that 65% of alleles were discernible by this method, and the alleles accounted for 68.75% of major type alleles sampled. Alignment of the exon 2 sequences of 7 haplotypes and the 20 alleles revealed 63 polymorphic sites, of which 48 sites were parsimony informative, and 15 sites were singleton variable. Among the variable sites, 13 of parsimony informative sites and 11 out of the singleton variable sites were unique to the Chinese indigenous breeds sampled. The sequences of the exon 2 shared 90.6%~99.5% homology to each other. The relative frequencies of nonsynonymous and synonymous substitutions of nucleotide at per site in the exon 2 were estimated, 14.64%±2.67% and 2.92%±0.94%, respectively; the former was highly exceeded the latter. The present study provided the basic data for investigation of the evolutionary mechanisms of MHC B-LBⅡ genes in chicken.