Objectives : The purpose of this study was to analyze the effect of outpatient cost sharing reduction on health care utilization of children under 6 years old. Methods : The data in this analysis was the health insurance claims data between August 2006 and July 2008. The study group was divided into two age groups, namely 0-5 years old and 6-10 years old. This study evaluated the impact of policy change on office visits per person and expenditure per visit. In order to do so, the double difference analysis is used. Results: The results showed that outpatient cost-sharing reduction has never really had a huge impact on office visits per person and expenditure per visit. Conclusions: This study showed that the outpatient cost sharing reduction for children under 6 years old policy is not working. Therefore, cost sharing of National Health Insurance by income class is needed.