An OLED display device includes a substrate, an active element array, at least one OLED, a light absorption layer or an optical scattering layer, and an encapsulation plate. The active element array and the OLED are disposed over an upper surface of the substrate. The OLED includes a first electrode, a second electrode, and an organic light-emitting layer. The first electrode is disposed on a side adjacent to the active element array, and the second electrode is opposite to the first electrode. Both the first and second electrodes have a high transmittance and a low reflection in a wavelength range of visible light. The organic light-emitting layer is interposed between the first and second electrodes. The light absorption layer or optical scattering layer is disposed between the OLED and the substrate. The encapsulation plate is disposed over the second electrode.