Diabetes mellitus is a heterogeneous metabolic disorder characterized by hyperglycemia. It is often associated with complications, such as cataracts. The purpose of this study was to investigate the effects of cactus pear juice on oxidative stress and cataract formation in alloxan-induced diabetic rats. Rats were divided into six groups, Group 1 untreated as negative control, Group 2 injected with alloxan only to induce diabetes as diabetic cataract positive control, Groups 3,4,5 and 6 injected with alloxan and given orally 1, 2, 3 and 4 ml concentrated cactus juice/rat/day, respectively. After 8 weeks, the animals treated with cactus juice showed a significant decrease in the level of blood glucose and lipid peroxidation in blood and lens, and a significant decrease in the concentration of lens Fas ligand, compared with negative control (group 1). Also, the treated groups showed significant increase in the level of reduced glutathione and the activity of superoxide dismutase and significant decrease in the levels of nitric oxide concentration. Slit lamp examination revealed that supplementation with cactus juice delayed the progression and maturation of cataract in the treated groups compared with positive control (group 2), which developed subcapsular cataract. The best result observed in Group 5, which was given orally 3 ml juice/rat/day. The data in the present study indicate that cactus juice is a rich source of natural antioxidants such as total phenolics, total flavonoids, vitamin C, vitamin E, β-carotene and total carotenoids. It can be concluded that regular consumption of cactus pear juice can protect the body from the oxidative stress and can attenuate the development of cataract as a complication of diabetes by reducing the level of blood sugar.