Insulin-like growth factor 1 receptor (IGF1R) is essential for the signalling of growth. In this study, we performed single nucleotide polymorphism (SNP) detection in the Japanese quail IGF1R coding region and an association study between SNPs and body weight in two lines (SS and LL) selected for large and small body weight. Of 21 SNPs obtained, a SNP at position AB292766:c.2293G>A led to the replacement of a valine with an isoleucine (V765I). The two lines were fixed for alternate alleles, with allele encoding valine fixed in the LL line. A significant effect of the SNP genotype was found on 10-week body weight (P < 0.01) and on 4- to 10-week and 6- to 10-week average daily gain (P < 0.05) in the F(2) family obtained from lines LL and SS. In six populations maintained in Japan or France, the frequency of allele encoding valine was higher than the allele encoding isoleucine.