An organic light emitting display device can include an organic light emitting diode (OLED), a driving transistor connected to an anode electrode of the OLED, a scan transistor, a digital-to-analog converter (DAC) and a sensing unit. The scan transistor is connected the anode electrode of the OLED and a data line. The DAC supplies a data voltage for displaying to the data line in a displaying period and supplies a data voltage for sensing to the data line in a sensing period. The sensing unit obtains an anode voltage of the OLED as a sensing voltage through the data line in the sensing period.