A mother substrate of an organic light emitting display device capable of effectively aging a plurality of organic light emitting display panels by sheet unit without scribing the panels is provided. In one embodiment, the invention relates to a substrate of an organic light emitting display device, including a plurality of organic light emitting display panels, a plurality of first wires configured to supply a pixel power source to the panels in a first direction, and a plurality of second wires configured to supply a reference power voltage to the panels in a second direction crossing the first direction, wherein voltage levels of the reference power voltage are set to different voltage levels relative to a position of panels on the substrate.