The oxidative damage and morphological changes of kidneys of rats exposed to cadmium (5 mg Cd /kg b.w) for 22 days and the protection using melatonin (10 mg/kg b.w) against cadmium toxicity was studied. Malondialdehyde (MDA) concentration as a lipid peroxidation indicator, activity of the antioxidant enzyme superoxide dismutase (SOD) and the concentration of glutathione (GSH) were measured in kidney homogenates. The morphological changes were investigated using both light and electron microscopes. The exposure to Cd led to an increase in the MDA levels and a decrease in both the activity of SOD and the concentration of GSH versus controls. In contrast, melatonin administration restored the previous changes to nearly the normal levels. Morphologically, Cd led to different histopathological changes such as loss of the normal cortical tissue, atypical tubules with hamorrhage, cellular degeneration and necrosis, fat globules and slought cells (urine cast) in the tubular lumens. Again, melatonin administration counteracts all changes and the tissue appears more or less normal. The rate of recovery was faster when melatonin was administered for treatment after the exposure of animals to cadmium than if the animals left without any treatment. The results suggest that melatonin may be useful due to antioxidant properties in combating free radical-induced oxidative stress and tissue injury resulted from cadmium toxicity.