The objective of this study was to determine the reference range for Creatinine in children<8 years old among Tehran citizens on the selectra 2 analyzer and manually with Jaffee alkaline picrate method. Pediatric reference ranges are important in order to determine whether a patient's result is normal or abnormal. Reference range on the selectra 2 system over this age are currently unavailable. The study used serum obtained from children admitted in diagnostic and health centers and the SPSS program T-test and Chi-square were used to analyze data. The results are given below: Creatinine: Age (Y): 0-2, Male: N=71, 0.46 mg/dl, SD=0.1; Female: N=61, 0.47 mg/dl, SD=0.1; Total: N=92, 0.467 mg/dl. Age (Y): 3-6, Male: N=89, 0.52 mg/dl, SD=0.001; Female: N=50, 0.53 mg/dl, SD=0.1; Total: N=139, 0.529 mg/dl. Age (Y): 7-8, Male: N=50, 0.58 mg/dl, SD=0.11; Female: N=37, 0.55 mg/dl, SD=0.11; Total: N=89, 0.572 mg/dl. Total: Male: N=210, 0.52 mg/dl, SD=0.11; Female: N=108, 0.53 mg/dl, SD=0.1; Total: N=318, 0.52 mg/dl. Serum Creatinine significantly increased with increasing in age and total body surface (P<0.05, 0.0001 respectively), while there has been no significant difference by sex, diet and fasting.