Introduction: L-carnitine can increase mitochondrial metabolism of long-chain fatty acids and defence against reactive oxygen species (ROS). This investigation was aimed to find out the improving effects of L-carnitine on renal oxidative stress and aerobic metabolism defect caused by acute unilateral ureteral obstruction (UUO).Methods: Male Sprague-Dawley rats (n=10 in each group) were lightly anesthetized by ether and, through a sterile surgical procedure, left ureter was doubly legated. L-carnitine (200mg/kg) and its vehicle (normal saline), in UUO+LC and UUO+NS groups, respectively, were twicely adminesterated I.P. before and after UUO-induction. The sham-operated and control groups were also included. After elapsing 24-hr of UUO-induction, both kidneys were removed and stored in -70°C. The kidney samples were assessed to measure the levels of ATP and ADP, for determining metabolism condition, and the levels of malondialdehyde (MDA) and ferric reducing/antioxidant power (FRAP), for evaluating redox state.Results: 24-hr of ureteral obstruction in UUO+NS group, caused increases in MDA (P<0.001) and ADP (P<0.05), but decreases in FRAP, ATP and ATP/ADP ratio in obstructed kidney with respect to those of the sham group (all P<0.001). The comparisons between UUO+LC and UUO+NS groups showed that MDA was lower (43.3±1.5 vs 51.4±1.9nmol/gKW, P<0.001), while ATP (1.53±0.13 vs 1.09±0.10 micromol/gKW, P<0.05), FRAP (4.23±0.30 vs 2.44±0.16 micromol/gKW, P<0.001) and ATP/ADP ratio (3.1±0.33 vs 1.6±0.1, P<0.01) were higher in obstructed kidney.Conclusion: Therefore, treatment with L-carnitine could markedly protect kidney against 24-hr UUO-induced reduction in oxidative metabolism and elevation in ROS.