Angiotensin receptor blockers (ARBs) and converting enzyme inhibitors (ACEIs) are have multiple indications other than hypertension. One of these indications is acute renal tissue injury. Comparative study between the protective effect of ARB pretreatment and treatment against an acute kidney injury is needed. Transient bilateral renal ischemia rat model was used to produce acute tissue injury and to test the protective effect of losartan. Serum creatinine, activated partial thromboplastin time (aPTT) and renal tissue injury score are evaluated. Losartan treated group had important more significant reno-protective effect than that of the losartan pretreated-treated group.