Abstract: Insulin-like growth factor I （IGF- I ）is the main regulatory factor for animal growth ,development and metabolism ,and it is the main mediator that the growth hormones activate the growth activity. The polymorphism at the exon 3 of IGF- I gene in Shanxi White Pig population was detected by PCR-SSCP. Three alleles ofA ,B and C were detected and six genotypes ofAA ,AB,A C, BB,BC and CC were found. The frequency of allele A was higher （0.549）than those of alleles of B and C,which were 0.173 and 0.278 respectively. In the case of genotype distribution, the frequencies of homozygote A A, heterozygote A B and A C （0.230,0.204, and 0.434 respectively ） were higher than those of other genotypes （less than ! 0% ）. The effects of mutation site on the birth weight, weaning weight and body weight, body height, body length, chest girth, back-fat thickness at the age of six months of Shanxi White Pig were analyzed by using the least square method. The results showed that the mutation site had significant influences on the body height of six-month pigs （P〈0.05）and the body height of six-month pigs with BC genotype was significant shorter than other genotypes （P〈0.05）. But the mutation site had no significant effect on other traits （P 〉0.05 ）.