insulin-like Growth Factor 1 (IGF-1) gene has been described in several studies as a candidate gene for growth. The present study attempts to identify associations between body weight traits and polymorphisms at 279 position of 5'UTR flanking region of IGF-1 gene in broiler chickens. Three hundred broiler chickens from two breeds (Cobb 500 and Hubbard F-15) were used in this study. A single nucleotide polymorphism (SNP) at 279 position of 5'UTR region of the IGF-1 gene was identified in 20.6 and 60.3% of Cobb 500 and Hubbard F-15, respectively, using the PCR-RFLP technique. Allele frequencies were 83.87 and 42.80% for the T allele and 16.13 and 57.20% for the C allele in Cobb500 and Hubbard-15 breeds, respectively. Genotype frequencies were 79.35, 9.03, and 11.61% in Cobb500 and 39.73, 6.16 and 54.11% in Hubbard F-15 for TT, TC, and CC genotypes, respectively. As related to mean body weight, different weekly results were noted between Cobb 500 and Hubbard F-15 according to genotypes during a period from 3-7 weeks of age. Within all genotypes, the mean body weights were higher (p>0.05) in males than females at 5 and 7 weeks of age. As related to body weight gain, Hubbard F-15 broilers were more affected by IGF-1 genotypes than Cobb500 broilers in the last three weeks of age. Also, male broilers were more affected by IGF-1 genotypes than female broilers. The results of this study demonstrated that the IGF-1 gene, to some extent, could be a candidate gene that affects growth in broiler chickens.