Strawberry tree (Arbutus unedo L.) is a Mediterranean plant which is used for centuries in folk medicine. The leaves contain high concentration of the phenols which have antioxidational, anticancerogenic, antimutagenic and antinflammatory effects. Phenols can stimulate the activity of antioxidant enzymes important for the endogenous fight with ROS, whose elevated concentrations can damage the cell and lead to various diseases. The aim of this study is to determine the antioxidant activity of Strawberry tree leaf aqueous extracts on: activity of antioxidant enzymes (SOD and catalase); lipid peroxidation and primary DNA damage in brain, liver and kidney cells of the Lewis rats breed of both sexes. Test groups of animals were treated with the aqueous extract of a strawberry tree leaf (200 mg / kg) per orally for 28 days. Reduction of catalase activity and a slight reduction of superoxide dismutase activity in rat kidney cells of both sexes were found. The treatment did not significantly affect the activity of catalase and superoxide dismutase, as well as the level of lipid peroxidation in the rat liver cells of both sexes. In the brain cells of the female rats, statistically significant increase of the catalase activity was observed. In brain cells of male rats statisticaly significant increased level of lipid peroxidation was recorded. Potential genotoxic effect of the aqueous leaf extract of strawberry tree is determined by using a comet assay in alkali conditions. Results indicate that there is DNA damage in the liver cells of male and female rats, very low DNA damage in the kidney cells of the males rats. Further studies are needed to determine the most appropriate dose and duration of treatment that will have the best therapeutic effect without adverse side effects.