Korea is one of the fastest aging country in the world. The increase in health expenditure is an inevitable problem in an aging country. We examined trend of benefit expenditure in National Health Insurance (NHI) by age group during 2001 to 2016. The benefit expenditure of NHI was 13.0 trillion won (2001) and 48.7 trillion won (2016); that is 3.76 times to 2001. This rapid increase was mostly due to people aged 65 and over. Proportion of beneficiaries aged 65 and over was 6.9% (2001) and 13.7% (2016), benefit expenditure per capita aged 65 and over was 279 thousand won (2001) and 960 thousand won (2016), and utilization days per capita aged 65 and over 21.44 (2001) and 30.23 (2016). This phenomenon was more pronounced in 75 or 85 aged and over. To contain the health costs for older people, the NHI system should be reformed.