Provided are an organic light emitting device (OLED) and a flat display including the OLED. The OLED includes an organic layer which includes a pixel electrode, an opposite electrode, and at least an emission layer between the pixel electrode and the opposite electrode, wherein the emission layer includes a long wavelength-blue emission layer emitting blue light having a long wavelength and a short wavelength-blue emission layer emitting blue light having a short wavelength. The long wavelength-blue emission layer is positioned in a location to enhance emission of blue light from the emission layer. The OLED can emit blue light with high efficiency and high brightness.