An organic light emitting display capable of displaying an image with uniform brightness is provided. The display includes a scan driver, a data driver, pixels, an initial power source line coupled to an initial power source, a bias power source line coupled to a bias power source, horizontal power lines, first switching elements, and second switching elements. Each of the pixels includes a driving transistor for controlling an amount of current that flows from a first power source. The bias power source has a different voltage from the initial power source. The first switching elements are coupled between the horizontal power source lines and the initial power source line. The second switching elements are coupled between the horizontal power source lines and the bias power source line. The second switching elements are configured to alternately turn on and off with the first switching elements.