Background and aim: various factors, in terms of faster diagnosis of acute renal failure have been studied so far, but these studies have been done mostly on adults. Therefore, in this paper we made a comparison of fractional excretion of sodium (FeNa), uric acid (FeUa) and urea nitrogen (FeU) in acute prerenal failure in children to find out which one is more sensitive in diagnosis of acute prerenal failure. Material and Methods: In a cross-sectional study, 5 CC blood was taken from 29 children of 1 month to 15 years old, diagnosed with acute pre-renal failure; the amount of creatinine, sodium, uric acid and urea nitrogen was measured in their plasma. After taking a standard urine specimen, all the mentioned items were measured in patients’ urine and put into the formula of FeNa, FeUa and FeU and compared. Results: In this study, 75.8% FeU, 68.9% FeUa and 58.6% FeNa are agreeable to prerenal criteria and the most sensitivity is assigned to FeU. Among the three groups, FeNa is more affected by treatment with diuretic. The difference between FeNa in the receiver group of normal saline and the receiver group of diuretic is more than those groups which did not receive any. Conclusion: Fractional excretion of urea nitrogen in children, especially in the receivers of diuretic is more sensitive in diagnosis of acute prerenal failure. Moreover, this index is more sensitive in diagnosis of acute prerenal failure than the other indexes.