The aim of the present study was to evaluate the changes in skeletal muscle which may occur after in ovo injection of Myo-Pro gene . A total number of 200 Fayoumi fertilized pure breed eggs were obtained from EL-Tkamoly poultry project - EL-Azab – Fayoum and divided into two equal groups. Control group, n= 100 that was injected with saline, and treated group n = 100 was injected with MyoPro gene. To check both possibilities, we examined the gastrocnemius muscle fibers number and diameter (cross sectional area). The results revealed that Chicken hatched from Myo-Pro injected eggs showed a significant increased muscle masses. This increase in muscle mass and subsequently meat production is due to hypertrophy rather than hyperplasia. From the obtained results, using Myo-Pro gene causing improvement in skeletal muscle fiber (diameter and number) in Fayoumi chicken.