Patient cost‐sharing change was implemented on August 1, 2007, for outpatient care in the clinic setting in Korea from copayment to coinsurance. This study aims to estimate the effect of the policy change on medical care usage and expenditure in older Koreans. By using national health insurance claims data from the Health Insurance Reimbursement Assessment Service, this study analyzed the entire 137 million claims for a total of approximately 4.1 million patients aged 60 to 69 years who had been diagnosed and/or treated for outpatient care in clinics from January 1, 2007, to December 31, 2008. Medical care usage was defined as the proportion of all beneficiaries in each group who visited clinics and the mean number of visit days per beneficiary. Medical care expenditure per visit day was expressed as total costs, reimbursed amount, and patient's out‐of‐pocket payment. Data on January through June of 2008 were analyzed as compared with the same months of 2007. Raw difference‐in‐difference and multiple regression analyses were performed. The interaction coefficients, which measured the impact of cost‐sharing change, was −0.078 in model 1 and −0.039 in model 2 (P < .0001). In conclusion, a cost‐sharing change from copayment to coinsurance reduced medical care usage and expenditure.