Insulin-like growth factor-1 (IGF1) plays an important role in muscle development in chickens. In this study, an F2 chicken population of 362 individuals, obtained from an intercross between high breast muscle yield line males and low breast muscle yield (LB) line females, was constructed for investigating the associations between IGF1 gene and breast muscle yields. The IGF1 sequence was investigated in the grandparents. There were no differences in the exon sequences. However, sequence analysis of the IGF1 promoter revealed a known single nucleotide polymorphism (g.570C > A) in LB line grandparents. PCR – restriction fragment length polymorphism was used for screening the F2 population, which was evaluated for body weight (BW), carcass weight (CW), breast muscle weight (BMW), and breast fillet weight (BFW). Significant associations with the polymorphism were detected for BMW, BFW, BMW% and BFW%, although there were no associations between the polymorphism and BW or CW. The allelic effect on BMW, BFW, BMW% and BFW% acted in additive and dominance modes. We confirmed that the g.570C > A polymorphism is significantly associated with breast muscle yields in the F2 population. Therefore, this polymorphism in the IGF1 gene may help improve breast muscle yields by marker-assisted selection.