Background: Exposure to arsenic through drinking water is a global health problem that causes multisystem toxicity, mainly by inducing oxidative stress and impairing cellular energy. Objective: We aimed to evaluate the effect of Quercus infectoria gall extract (Qi) against oxidative stress induced by sub-acute exposure to arsenic. Methods: The plant galls were extracted with methanol and were used for the determination of total phenolic content using Folin-Cio calteu reagent. Male Wistar rats were randomly divided into 8 groups of 6 animals and treated for 30 days. Negative and positive control groups received, respectively, normal saline and sodium arsenite (5.5 mg/kg) by gavage. Treatment groups received three doses of Qi (200, 400, and 600 mg/kg/day) by intraperitoneal injection 2 h. after oral administration of normal saline or sodium arsenite (5.5 mg/kg) (As-Qi). After 30 days, all animals were anesthetized with ketamine/xylasine and 2 mL of blood was taken for measurement of total antioxidant capacity using ferric reducing antioxidant power (FRAP), lipid peroxidation (measurement of malondialdehyde (MDA)) and protein carbonylation of plasma. Results: Total phenolic content of the plant was determined to be 5.78± 0.23mg gallic acid equivalent/ g dried extract. The results of pharmacological studies indicated that in arsenic treated animals, a significant decrease in TAC, increase in lipid peroxidation and protein carbonylation happens compared to control group. Co-administration of Qi (600 mg/kg) with arsenic significantly increased TAC compared with arsenic group (0.245 ± 0.007 versus 0.183 ± 0.027 for arsenic) (p<0.05), while the serum MDA level (1.880± 0.499 versus 2.795 ± 0.112 for arsenic) and protein carbonylation were decreased in this group compared with arsenic treated animals (0.128± 0.007 versus 0.159 ± 0.009 for arsenic) (p<0.01). In non-treated arsenic animals (NTAS), all three doses of Qi improved oxidative stress markers. Conclusion: Arsenic disrupt cellular antioxidant defense through overproduction of ROS and the Qi galls are able to revert some of these oxidant activities of arsenic. Previous studies have reported antioxidants in the plant and the present work can conclude that antioxidant effect of Qi is useful against happened oxidative stress in arsenic treated animals. other: no