Abstract: In the experiment,PCR-RFLP technique was used to detect the diffrences of the resistant and sensitive alleles distribution of S631N locus of Mx gene in twelve Chinese indigenous chicken populations.The results showed that the PCR-RFLP technique properly detected the mutation between resistant allele A and sensitive allele G.Among the twelve populations,the average frequencies of resistant allele A and sensitive allele G were 0.304 and 0.696,respectively.The average value of observed heterozygosis and Shannon′s index at this locus were 0.657 2 and 0.524 0,respectively.Except for Xianju chicken,the other eleven populations were all in Hardy-Weinberg equilibrium at this locus (P>0.05).Except for Baier chicken,the EwensWatterson test indicated that this locus was neutral in all the other populations.The dendrograms based on allele frequency divided the twelve indigenous chicken populations into three clusters,which reflected the difference and advantage of Mx antiviral property in twelve indigenous chicken populations.