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Abstract Background & aim: The genus Pistacia belonging to the Anacardiaceae family which consists of 15 species only three species of which, namely Pistacia vera, Pistacia Atlantica, ,and Pistacia Khinjuk grow in Iran. The aim of present study was to investigate the antioxidant activity of Pistacia Atlantica fruit hydroalcoholic extract in Yasuj. Methods: In the present experimental study, the extract was carried out with two, maceration and Soxhlet methods. For in vitro antioxidant assay, (trolex equivalent antioxidant capacity (TEAC), Diphenyl-picrylhydrazyl (DPPH) phosphomolybdenum (PMB) was conducted. For determination of antioxidant components, total phenolic and flavonoids contents were analyzed in in vitro assay. To evaluate the antioxidant activity by In Vivo method, the hydro alcoholic extract, having the most antioxidant activity, was used. 24 Wistar rats with the weight 250-300 g were examined that were randomly divided into 4 groups of 6. Group 1 (control group) used distilled water by oral route with amount of 0.5 ml/kg. Groups 2, 3, and 4 used 100, 200, and 400 mg/kg of Pistacia Atlantica hydro alcoholic extract by gavages, respectively. After 4 weeks of treatment, blood samples were collected by heart puncture. Catalase enzyme activity, Mallon dialdehyde and Ferric reducing antioxidant power were measured in rats’ plasma. ANOVA was used for data analysis. Results: Methanol extract of Pistacia Atlantica contained the maximum amount of phytochemical and antioxidant activities. A significant decrease was observed in serum malondialdehyde (MDA) of the treatment group compared to the control group (P<001).There was a significant increase in level of Catalase and Ferric reducing antioxidant power (FRAP) of treatment groups compared to the control group (P<001). Conclusion: Pistacia Atlantica extracts depending on type and system of extraction contains different antioxidant potential. Key words: Antioxidant Activity, Pistacia Atlantica, Catalase, MDA, lipid Peroxidation