Disclosed is an organic light emitting display device. The organic light emitting display includes a display panel including a plurality of pixels, which are respectively formed in a plurality of pixel areas defined by crossings of a plurality of gate lines and a plurality of data lines, a plurality of sensing lines, and a plurality of second gate voltage lines connected to the plurality of pixels, a panel driver to drive the display panel in a display mode or a sensing mode, to sense a threshold voltage of at least one transistor to generate a sensing data in the sensing mode, and generate a second gate voltage data in the display mode, and a voltage supply unit to generate a second gate electrode voltage corresponding to the second gate voltage data, and apply a second gate electrode voltage to a second gate electrode of the transistor.