An organic light emitting display device includes a display part including a plurality of scan lines, a plurality of data lines, a plurality of power source lines, and a plurality of pixels each including an organic light emitting diode, a driving transistor coupled to the organic light emitting diode and to a power source line of the power source lines, and a switching transistor coupled to a scan line of the scan lines and to a data line of the data lines, and a sensing driver configured to sample a sensing current from the power source line while a sensing data voltage is applied to one of the pixels, and to calculate a threshold voltage value of the driving transistor using the sensing current in a sensing mode.