AIM: To investigate the protective effects of losartan on renal ischemia-reperfusion injury in rats. METHODS: Rats were divided into four groups: normal control, sham-operation, renal ischemia-reperfusion model and losartan groups. Losartan was fed by ig to the rats as early as the day two weeks before renal ischemia-reperfusion. After 1 h renal ischemia, 1 h and 24 h renal ischemia-reperfusion, the content of malondialdehyde (MDA) and activity of superoxide dismutase (SOD) were detected in the homogenate of renal tissues. RESULTS: Compared with normal control and sham-operation groups, the MDA content in model, losartan groups were significantly higher (P<0.01) and SOD activity in model group was profoundly lower (P<0.05). After 1 h and 24 h reperfusion, the MDA content in losartan group lowered from (9.5±0.4) nmol·mg -1pro and (11.9±0.9) nmol·mg -1pro to (7.7±1.0) nmol·mg -1pro and (9.2± 0.5) nmol·mg -1 pro. Compared with model group and SOD activity in losartan group compared with model group in creased from (48±11) NU·mg -1pro and (18±4) to (79±4) NU·mg -1pro and (48±4) NU·mg -1 pro(P<0.05). CONCLUSION: Losartan can relieve the damage caused by activated oxygen free redical increased significantly in acute renal ischemia-reperfusion rats.