Diabetes mellitus is a chronic metabolic syndrome characterized by chronic hyperglycemia that occurs due to the relative and / or absolute deficiency of insulin. Oxidative stress can damage macromolecules and DNA causing dysfunction of cells and tissue damage. Increased oxidative stress is a factor that ultimately leads to the development of type 2 diabetes. Some studies have shown that antioxidant treatment can prevent or lessen the cardiovascular complications of diabetes. Silver Birch (lat. Betula pendula) is a deciduous tree that grows throughout Europe and Asia. In traditional medicine throughout the world for many years people have been used extracts from the bark. In the literature there are no data on antioxidant effect of aqueous extract of the leaf of Betula pendula. The aim of this study was the examination of such effect. Water extract of the leaf of Betula pendula contains flavonoids, phenols and phenolic acids. HPLC phytochemical analysis confirmed that the main component in the aqueous extract of the leaf of Betula pendula is flavonoid rutin while the other components are present in lower concentrations. The experiment was using Hep G2 cell culture. These are human, epithelial cells of hepatocellular carcinoma. Oxidative stress was induced by treating the cells with 30 mM glucose solution. The concentrations of aqueous extract of the leaf of Betula pendula amounted to 0.05 mg / mL, 0.1 mg / ml and 0.5 mg / ml.The concentration of glutathione, free thiol groups and the enzyme activity of glutathione-S-transferase were measured by spectrophotometric methods. The results were statistically analyzed in the statistical program MedCalc 14.8. and Microsoft Office Excel 2010. Antioxidant activity of an aqueous extract of the leaf of Betula pendula is shown only at a low concentration (0,05 mg / ml) while high concentrations may even have prooxidant effect.