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Objective: Ocular morbidity is widely observed when radiotherapy includes the orbit.Oxidative stress generated by irradiation is responsible for this complication. In differentstudies, it has been shown that melatonin has antioxidative properties and a radioprotectiverole. The aim of this study was to evaluate the antioxidant role of melatonin againstradiation-induced oxidative injury in rats' lenses after total cranial irradiation.Materials and Methods: Thirty-six adult female Sprague-Dawley rats were divided intosix groups. Group I was the control group, group II only received total cranial gamma irradiationof 5 Gy, group III was exposed as the second group but at the dose of 8 Gy, groupIV received 30 mg/kg melatonin 30 minutes prior to radiation plus total cranial irradiationof 5 Gy plus 5 mg/kg melatonin daily through intraperitoneal injection for ten days afterirradiation, group V was treated similar to the fourth group, i.e. received irradiation plusmelatonin, but at the dose of 8 Gy, and group VI only received melatonin (30 mg/kg onthe first day and 5 mg/kg on the following days). Ten days after irradiation, all rats weresacrificed and their eyes were enucleated to measure the biochemical parameters i.e.malondialdehyde (MDA) and glutathione (GSH).Results: The levels of MDA in rat lenses increased and the levels of glutathione in lensesdecreased after gamma ray irradiation but these parameters were still within normal limitsin rats that received melatonin.Conclusion: It could be concluded that melatonin is useful in preventing radiation-inducedoxidative injury due to its antioxidative and free radical scavenging properties.