Korea Background: The purpose of this study is to analyze the effects of differential coinsurance policy on prescription drug coverage of outpatients by types of medical institutions. Methods: In this study, we used a sample cohort database of the National Health Insurance Service and frequency analysis and marginal logistic regression model using generalized estimating equation were used for statistical analysis. Results: The summary on the major research is followed. First, about 16% of patients who used only tertiary or general hospital due to 52 ambulatory care sensitive conditions before policy implementation moved to hospitals and clinics. However, about 57% of them still use tertiary or general hospital. Second, the factors influencing the utilization of hospitals and clinics after the implementation of the policy were gender, age, and income level. As a result, the policy is effective to reduce the medical use of outpatient mental patients in tertiary or general hospital, but the effect is not significant. Conclusion: Therefore, in order to achieve the purpose of the policy for establishing the health care delivery system, it is necessary to adjust the co-payment so as to feel the burden on the co-payment when the outpatient for 52 ambulatory care sensitive conditions is used at the tertiary or general hospital.