This study empirically investigates the existence of a cointegration relationship between income inequality and economic growth using Korean time-series data. The income quintile ratio is adopted as the variable representing income inequality. This variable is defined as the ratio between the average income of the top 20% and the bottom 20% income brackets, based on household income data obtained from Statistics Korea. The cointegration test result shows that there is a long-run equilibrium relationship between income inequality and economic growth, and that income inequality is positively correlated with economic growth over the period 1990-2017.