This study is designed to estimate an appropriate level of patient`s cost-sharing for oriental medical services in the Korean National Health Insurance. The findings of this study can be summarized as follows: 1) The current co-payment system for oriental medical services does not reflect its cost structure in clinical practice due to inconsistency of cost-sharing plan in the NHI. 2) Both oriental medical institutions and their patients, as a result, are at a relative disadvantage in financial burden, compared with other services. 3) The substantial proportion of patients` cost-sharing depends on the amount of co-payment and the range of medical cost that a flat rate is applied to. 4) The extension of the range doesn`t make any substantial decrease in patient`s cost-sharing. 5) The fixed amount of co-payment is more sensitive than a range to total variations of patient`s cost-sharing. Based on the above, the budget impacts of a new co-payment system were estimated for each co-insurance rate, according to given scenarios. The results range from -59 billion Won(-8.5%) to 16 billion Won(2.3%).