Abstract: The present study was conducted to investigate the effect of L-Arginine (Arg) supplementation on protein oxidation as well as Paraoxonase (PON) activities in rats received either normal or high cholesterol diet with or without 3% Arg in drinking water. Hypercholesterolemia (HC) was induced in rats by feeding diet containing cholesterol 5%, cholic acid 1% and propylthiouracil 0.5%. The spectrophotometric analysis methods were used for determination of lipid profiles as well as oxidative stress biomarkers in the plasma and liver tissues of rats. The results of current study revealed that the feeding of rats with Hypercholesterolemic Diet (HCD) resulted in significant increased of Atherogenic Index (AI) by 256% in respect to control rats. Arg supplementation to rats with HCD resulted in decrease of AI by 152% comparison with rats received HCD. Moreover, administration of Arg with normal or HCD attenuates the protein oxidation as well as lipids peroxidation in compared to intake of HCD alone. As a result of HCD feeding, plasma arylesterase (ARE) activity was decreased by 30% while in liver it decreased by 36%. Furthermore, paraoxonase activity (PON1) was decreased 42 and 74% for plasma and liver, respectively. On the other hand, the treatment with Arg ameliorates both activities in the plasma and liver in comparison with HCD. Arg preserve thiols and nitric oxide level, thereby reducing oxidative stress associated with increased cholesterol level. This may be related antioxidant effect of this amino acid. Therefore, Arg has beneficial effects in the treatment of HC thruogh decreases the proteins oxidation as well as preservation of high density lipoprotein function through maintaining PON activity.