Abstract: The polymorphism of the insulin-like growth factor 1 (IGF-I) gene in Nanyang, Luxi cattle, and Chinese Simmental was analyzed by PCRSSCP and PCRRFLP. The results showed that the polymorphisms were not detected by PCRSSCP and PCR-RFLP in the 5′flanking region, and the exon 5 of the IGF-I gene. And three genotypes, AA, AB, and BB, were detected in the exon 2 of the IGF-I gene. The polymorphism fragments were cloned and sequenced. The sequencing results indicated that there were three single nucleotide mutations: A→G at 35 bp, C→T at 248 bp, A→G at 256 bp in the exon2 of the IGF-I gene, but the mutations at 35 bp and 248 bp were missense mutations. The mutation at 256 bp resulted in amino acid change: Glu→Gly.