Provided is an organic light emitting diode (OLED) display device including a substrate on a front side of the OLED display device that is coupled to an encapsulation substrate on the back side of the OLED display device. An interconnection line is disposed in a predetermined region of the encapsulation substrate corresponding to a portion of the substrate on which no interconnection lines are disposed. Alternatively, a common power supply line is disposed only on the encapsulation substrate. As a result, a dead space in a display region of the substrate can be reduced so that other lines can be disposed in an interconnection line region of the substrate, and the display region can be further expanded. Also, since a wide interconnection line can be disposed on the encapsulation substrate, line resistance is decreased and a voltage drop can be reduced.