Over the past decades, financial markets have been integrated across countries while income inequality has increased in most countries. This paper studies the effect of financial market integration on income inequality and investigates whether the effect varies with the degree of financial market development. We find an empirical evidence that financial market integration and financial market development interact to change income inequality. Specifically, the effect of financial market integration on income inequality is nonlinear, and the degree of financial market development plays an important role. Opening financial market worsens income inequality in the countries holding the underdeveloped state of financial market, however, the effect of capital account openness on income inequality is statistically insignificant in the countries with developed financial market.