In this study, 28 Wistar Albino male rats were randomly divided into four equal groups. 2,3,7,8-tetrachlorodibenzo-p- dioxin (TCDD) was intraperitoneally administered at the dose of 2 μg/kg/week, quercetin was administered at the dose of 20 mg/kg/day by gavages, and quercetin+TCDD were intraperitoneally administered at the doses of 20 mg/kg/day and 2 μg/kg/week, respectively. All applications were performed for 8 weeks. At the end of the eighth week, the rats were sacrificed and their heart and vascular tissues were taken for biochemical analysis (reduced glutathione (GSH), glutathione peroxidase (GSH-Px), catalase (CAT), superoxide dismutase (SOD) and thiobarbituric acid reactive substance (TBARS) levels) by spectrophotometric method. As a result of the study, TCDD significantly decreased antioxidant activities and increased lipid peroxidation in rats. In contrast, quercetin significantly prevented the toxic effects of TCDD via increasing SOD, CAT, GSH and GSH-Px levels but decreased the formation of TBARS. Therefore, it can be suggested that quercetin has the potential for treatment against the toxicity caused by TCDD or other environmental contaminants and can decrease the risk of mortality due to cardiovascular diseases, especially in humans.