Genetic polymorphisms along with expression patterns of IGF-I gene were studied in 300-day-old chicks of three different broiler strains (Cobb, Avian, and Ross) with 100 birds each. Blood samples were collected from chicks of each strain for DNA extraction and serum analysis of IGF-I. PCR-PstI digestion of 621-bp for a fragment of 5′ untranslated region of IGF-I gene revealed a monomorphic pattern for genotype AA; where one undigested fragment (621-bp) was attained in all strains. Liver of randomly selected ten female chicks from each strain was collected for RNA extraction and quantitative real time PCR (RT-PCR) genetic assessment. Expression patterns of IGF-I gene revealed a significant up-regulation in Avian than Cobb and Ross breeds as shown by significant lower values of ΔCT. Serum analysis results were in coincidence with IGF-I gene expression; where Avian strain had a higher level of IGF-I than Cobb and Ross strains. It could be concluded that genetic IGF-I-PstI locus polymorphism could not be used as a genetic marker (MAS) for growth traits in commercial broiler strains. However, changes in IGF-I expression patterns could be a proxy marker to follow up and improve growth performance of broiler chickens.