This study was to determine the inappropriate drug use in pediatric outpatients who received 2 or more prescriptions on the same day. Retrospective drug utilization reviews (DURs) were implemented to samples obtained from national health insurance claims data during December 2008 to February 2009, using 5 DUR criteria (duplication, drug-drug interaction, drug-disease interaction, drug-age contraindication, incorrect dosage) established in the Drug Information Framework (DIF)-$Korea^{TM}$, DUR program. Among 38,451 claims analyzed in the study, 74.7% had more than one conflicts in the 5 DUR modules. Among 16,472 patients analyzed, 49.6% had conflicts with duplication criteria composing of ingredient duplication (23.3%) and therapeutic class duplication (39.6%). Incorrect dosages were found in 73.6% of patients and under-dosage conflicts accounted for 59.9%, which was higher than over-dosage conflicts (38.3%). In this study, inappropriate drug prescriptions such as under-dose, pediatric contraindication and therapeutic duplication were prevalent in pediatric outpatient settings, suggesting much more awareness to the society, to prevent drug related problems in a vulnerable pediatric group.