An organic light emitting diode (OLED) display device and a manufacturing method thereof to improve a luminous character are provided. The OLED display device includes a first transistor, a second transistor and an OLED. An image is displayed by applying a driving current to OLED through the first transistor and the second transistor. The thickness of the gate insulating layers of the first and the second transistor are different. The OLED is provided with the sufficient driving current to improve the luminous character without decreasing emissive area.