Abstract: This study was designed to systematically analyze the genetic polymorphism and variability of NGB gene exon 3 of 283 Simmental cattle hybrid taxon in Gansu Linze, Ganzhou, Wuwei, Jinchang, and Gaotai. DNA fragment containing the exon 3 and part of intron of NGB gene was amplified and genotyped using PCR single-strand conformational polymorphism（SSCP） method. Representative alleles were sequenced for verification of their variations in DNA sequences. The results displayed that there were 5 alleles（A, B, C, D and E） detected, combined five genotypes as AA, AB, AC, AD and AE. Among them, samples from Ganzhou, Wuwei and Jinchang were detected AA and AB genotypes, AA and AE genotypes in Gaotai and AA, AB, AC and AD genotypes in Linze. Allele A was the predominant allele and AA was the predominant genotype in five breeds. Sequence of the SSCP showed 6 mutations in the DNA fragment（75 bp C→T, 78 bp C→G, 128 bp G→A, 214 bp G→A, 232 bp C→T, and 233 bp G→A）. In which, C→T at 75 bp and C→G at 78 bp were located in intron, while the other mutations were located in exon. G→A mutation at 214 bp, C→T mutation at 232 bp and G→A mutation at 233 bp were lead to Gly→Ser, Arg→Trp and Arg→Gln, respectively. Chi-square testing indicated the three gene mutation were all in Hardy-Weinberg equilibrium（P> 0.05）. Population genetics analysis showed the polymorphism information content were 0.0582, 0.0196, 0.0196, 0.0161 and 0.0159 in Linze, Ganzhou, Wuwei, Jinchang, Gaotai, respectively, which was at low polymorphism（PIC <0.25）.

Key words: Simmental cattle hybrid taxon, NGB gene, exon, genetic variation