Under the assumption that the average income of an age group isindependent of the population weight of that group, this study aims to estimatethe effects of changes in population structure on income inequality using thesquared coefficient of variation (SCV) with the Household Income andExpenditure Survey between 1982 and 2008.The SCV dropped significantly from 0.328 to 0.208 during 1982～1994period. The sharp decrease in the SCV was mostly due to the change inincome distribution. To the contrary, the changes of population structure andincome distribution explain 14.9% and 85.1% of SCV changes respectively,during 1994～2008 period. A simulation result suggests that population agingwill increase income inequality by 7.5% by 2018 and 27.5% by 2050, evenwithout any further change in income distribution.