The aim of this study was to evaluate the relationship between fish size and expression of insulin like growth factor1(IGF-1) in musculature and cytochrome P450 1A (CYP1A) in liver tissues using semi-quantitative PCR. Mugil capito with different sizes obtained from three different regions (AlHamol, Al-Riad and Sidi Salem) at Kafr El Sheikh Governorate, Egypt were used. The results of IGF-1 and CYP1A genes expression analysis revealed that small sized fish at Al-Hamol and Al-Riad regions were higher than those obtained from Sidi Salem region. Meanwhile, IGF-1 expression in large sized fish at Sidi Salem region was strongly significant compared to all different sized fish in different regions. However, the CYP1A expression in medium sized fish at Sidi Salem region was strongly significant compared to all different sized fish in different regions. It can be concluded that pesticides pollution had effect on the fish health, which was reflected on the size and expression of IGF-1 and CYP1A genes.