The present study aimed at investigating the genetic and hormonal differences between a low growth rate chicken breed (a native breed: Fayoumi chicken) and a high growth rate chicken breed (Cobb chicken). A total number of 100 one-day-old Fayoumi chicks and 100 one-day-old Cobb chicks were used. Chicks of each breed were allocated into three equal replicates. The growth parameters [body weight, Body weight gain (BWG) and Feed conversion ratio (FCR)], genetic expression of some growth related genes (IGF1, ghrelin and Myostatin gene) and plasma level of some growth related hormones (Insulin, T3, T4 and corticosterone) were recorded. The obtained results revealed that, Cobb chicken had significantly higher body weight, BWG and feed intake than Fayoumi chicken but the FCR of Fayoumi chicken was higher than that of broiler chicken. Cobb recorded significantly lower plasma level of corticosterone, T3 and T4 than Fayoumi chicken while Insulin is higher in cobb chicken. Cobb recorded highly significant values of IGF1 and ghrelin Gene expression while myostatin gene expression was higher in Fayoumi chicken than in Cobb. From the obtained results could be concluded that, the observed high growth rate in cobb chicken may be attributed the difference gene expression related growth as well as hormonal difference