Past studies have already determined that selenium is very effective in alleviating oxidative damage caused by various abiotic stresses in plants. This study investigated the effects of selenium on the growth and physiological traits of basil under arsenic toxicity. The results showed that growth parameters including root and shoot length and root and shoot weight under arsenic toxicity, especially at high concentrations, were significantly reduced compared to the control plants. Also, in severe arsenic toxicity, the content of photosynthetic pigments, nitrogen, and protein concentrations decreased and the activity of catalase and superoxide dismutase enzymes increased compared to the basil plants without stress. Selenium foliar spray, especially at a concentration of 5 mg/l on plants, both under stress and without stress, led to increased growth parameters, photosynthetic pigments, nitrogen, and protein content. In addition, the use of sodium selenate at low concentrations reduced the activity of antioxidant enzymes and at high concentrations increased their activity under arsenic toxicity compared to control plants. In general, it seems that selenium has reduced the toxic effects of arsenic in basil by enhancing its antioxidant activity and improving plant growth.