Quercetin (QUR) is a polyphenolic phytochemical flavonoid, it is a strong reactive oxygen species (ROS) scavenger and good metal chelator, rich in phenolic hydroxyl groups that have strong antioxidant activity. For the present study, the strong antioxidant activity of QUR on several biochemical parameters in blood and liver of male rats exposed to high fat diet (HFD) induced non alcoholic steatohepatitis (NASH), were investigated. Sixty white male albino rats weighting 150 - 200 gm were used in this study. The rats were divided into four equal groups. 1) Normal group: received no drugs. 2) NASH group: received HFD daily for 12 weeks. 3) NASH + Quercetin group: received HFD daily for 3 months then QUR treatment (50 mg/kg body weight) through intraperitoneal route (i.p) daily for 10 weeks after induction of NASH. Blood and liver samples were collected from all animal groups two times, after the 6 th and 10th week of treatment period. Serum was separated for determination of serum Alanine Aminotransferase (ALT), Aspartate Aminotransferase (AST), Alkaline Phosphatase (ALP) and Gamma Glutamyl-Transferase (γ-GT) activities and Albumin, Total Protein, Total Bilirubin, Total Cholesterol and triglycerides concentrations. Levels of reduced glutathione (GSH) and activities of Superoxide Dismutase (SOD) and Catalase (CAT), were determined in liver tissues. Extent of oxidative stress was also assessed by hepatic lipid peroxides (MDA). The obtained results revealed that, HFD supplementation exhibited a significant increase in: 1) serum ALT, AST, ALP and γ-GT activities, in addition to Total Bilirubin, Total Cholesterol and triglycerides concentrations. 2) Liver MDA concentration. QUR administration in NASH rats exhibited a significant increase in all mentioned parameters. On contrast, HFD supplementation exhibited a significant decrease in serum Albumin and Total Protein, also marked depletion in liver GSH, CAT and SOD, were observed. QUR administration in NASH rats exhibited significant increase in all mentioned parameters. From the obtained results, it could be concluded that, the potential of QUR as natural antioxidant act as a powerful agent against the harmful effects of NASH