This paper examines the effect of population ageing on Korean tax-benefit structure. This paper estimates a simple net tax function using National Survey of Tax and Benefit (NaSTaB), controlling for changes in the household head’s age structure. We find that the progressivity of the net tax function more than doubled between 2007 and 2019, while about 30% of the change accounted for by population ageing. The effect of population ageing on the progressivity is mainly through government transfers. We also find that population ageing explains about 40% of the rise in the estimated income redistribution effect of Korean tax-benefit structure.