The present study was planned to investigate the effect of thermally oxidized palm oil on the broiler performances, liver gene expression, lipid profile and oxidative stress markers. A total number of 150 one d-old Cobb 500 broiler chicks were randomly divided into three treatment groups. The first group was served as control and fed the basal diets with tap water. The second group fed the basal diet supplemented with 5% fresh palm oil, the third group fed the basal diet supplemented with 5% thermally oxidized palm oil. The experiment continued till chicks were 42 d old. Body weight, feed consumption, feed conversion ratio was estimated.  Estimation of the effect of different treatments on the liver gene expression, Estimation of the lipid profile in serum, Estimation of the cholesterol level in the liver tissue. Correlation between the cholesterol level in both serum and liver tissue. Determination of oxidative stress markers in serum. The results showed that the supplementation of thermally oxidized palm oil decrease the body weight, reduce feed consumption, and increase the feed conversion ratio. Thermally oxidized oil cause a significant increase in the PPAR-α gene expression in liver tissue, increase the cholesterol concentrations in serum and liver, elevate triglycerides in serum and elevate the oxidative stress markers..