To investigate the possible protective effects of aminoguanidine (AG ) on lung damage in whole body irradiated rats. To evaluate the biological damage of radiation on rat lung tissue, lipid peroxidation products were measured using biochemical parameters. Thirty Wistar albino rats were divided into three subgroups: control (C) , irradiation alone (RT), and RT + AG combined. After sacrificing the rats, antioxidant enzymes catalase (CAT), superoxide dismutase (SOD) and glutathione peroxidase (GSHPx) activities and malondiadehyde (MDA), nitric oxide (NO) levels were evaluated in lung tissue. Administration of AG resulted in an increase in the activities of CAT, SOD and GSHPx in the lungs. All were reduced after radiation. In addition, AG administration resulted in a decrease in both NO and MDA levels in lung compared with the irradiated group. Amnoguanidine increased the endogenous antioxidant defence mechanism in rats and protected the animals from radiation-induced lung toxicity. Moreover, AG may protect against ionizing radiation-induced lung damage because of its antioxidant effect.