Heavy metals reduce the plant growth and adversely affect plant performance potential. Heavy metals also induce the formation of reactive oxygen species leading to cell damage. Plants deal with heavy metal stress by activating enzymatic and non-enzymatic antioxidant systems such as Superoxide Dismutase which converts superoxide anion to hydrogen peroxide. Then Peroxidase and Catalase convert hydrogen peroxide to water. Another method employed by pl-ants to deal with heavy metals is mycorrhizal symbiosis. In this study, mycorrhizal and non-mycorrhizal barley seedlings (Hordeum vulgar), var. Rayhan, grown in a greenhouse were treated with four concentrations of nickel (0,100,200 and 400 µg/g). Results showed greater antioxidant activity in mycorrhizal plants compared with non-mycorrhizal plants.  Also, it was determined that the accumulation of nickel in roots of mycorrhizal plants was greater compared with non-mycorrhizal plants.