Diabetic cataractogenesis is a complex process connected with hyperglycemia and oxidative stress. Free radicals induce many unfavorable changes in the activity of the antioxidative enzymes and may also lead to oxidative damage. Since diosmin, a plant-derived flavonoid, reveals antioxidative activity, the aim of the study was to investigate if this substance may counteract the oxidative stress in the lenses of diabetic rats. The study was conducted on the male Wistar rats with streptozotocin-induced type 1 diabetes. After the administration of diosmin at the doses of 50 and 100mg/kg for 4 weeks the oxidative stress markers in the lenses of these rats were evaluated. Tested markers included: activity of superoxide dismutase, catalase and glutathione peroxidase, as well as levels of total and soluble protein, level of glutathione, vitamin C, advanced oxidation protein products and malonyldialdehyde. The obtained results indicate that the administration of diosmin to the diabetic rats counteracted the unfavorable changes induced by diabetes in the lenses. It can be assumed that diosmin may be a promising compound in prevention or delaying the cataract formation during diabetes.