Aim: To investigate whether erdosteine supplementation following selenite exposure affects oxidant-antioxidant equilibrium and prevents cataract formation in rat pups. Methods: Thirty-nine Wistar-albino rat pups were divided into 3 groups. In Group 1 (n=16) only s.c saline was injected. In Group 2 (n=10) subcutaneous (s.c.) sodium selenite (30 nmol / g body weight) was injected on postpartum day 10. In Group 3 (n=13) s.c. sodium selenite (30 nmol/g body weight) were injected on postpartum day 10 and oral erdosteine (10 mg/kg body weight, daily for one week) was administered by gavage thereafter. The development of cataract was assessed weekly. The density of cataract was graded by slit-lamp biomicroscopy. On day 21, the blood was collected and lenses were removed. Oxidative stress index (OSI) and total antioxidant capacity (TAC) were determined in the lenses of the rat pups. Paraoxonase-1 (PON 1) activity was determined in the sera. Results: All of the lenses of rat pups in Group 1 remained clean. All rat pups developed dense nuclear opacity in Group 2. Eight out of 13 rat pups developed slight nuclear opacity in Group 3. Differences among the groups were statistically significant (p<0.05). Group 2 lenses had higher mean OSI level than that of Group 3 lenses (p=0.003). Group 2 lenses lower mean TAC levels than that of Group 3 (not significant). Mean PON 1 level of Group 2 was lower than that of Group 3 (p<0.05). Conclusion: Erdosteine diminishes the incidence of cataract due to its protection of the antioxidant defense system.