An organic light emitting display capable of improving display quality. The organic light emitting display includes effective pixels positioned in an effective display unit, at least one dummy pixels positioned in a dummy display unit in order to generate light with predetermined luminance, at least one photodiodes arranged on the dummy display unit to be adjacent to the dummy pixels, and a sensing unit for extracting first resistance information from organic light emitting diodes (OLED) included in the effective pixels, extracting second resistance information from OLEDs included in the dummy pixels, and extracting luminance information corresponding to the second resistance information from the photodiodes.