Background and Objectives: Serum amylase increases and its excretion fraction decreases in patients with renal failure. Excretion fraction can be used as a diagnostic way in individuals with acute renal transplant REJECTION. In this study, the association between amylase excretion fraction and acute renal transplant REJECTION, was investigated in pediatrics. Methods: in this case-control study, serum and urine amylase and serum and urine creatinine, were measured in children without (30 cases) and with (30 cases) acute renal transplant REJECTION, and their amylase excretion fraction was determined. Sonography of kidney and urinary tract, was used to rule out the obstruction due to surgical manipulation. To rule out cyclosporine intoxication and urinary tract infection (differential diagnostic factors of acute renal transplant REJECTION), serum cyclosporine and urine CRP were assessed, respectively. Data analysis was performed using t-test and logistic regression test. Results: In children with acute renal transplant REJECTION, variables of urine creatinine (20. 1± 5. 5 vs 15. 9± 4. 7, p=0. 002), urine amylase (744. 9± 376. 6 vs 584. 8± 218. 3, p=0. 049), and amylase fraction excretion (238. 7± 118. 4 vs 96. 112± 2. 5, p<0. 001), were significantly higher, as compared to the group without acute renal transplant REJECTION. Based on the multiple logistic regression analysis, among the measurable variables, only amylase fraction excretion, urine amylase and urine creatinine, only amylase fraction excretion and urine creatinine could independently predict acute renal transplant REJECTION. Conclusion: The findings of the current study showed that accurate assessment of the urine creatinine and amylase fraction excretion, can predict the probability of acute renal transplant REJECTION in children.