An organic light emitting display and a driving method thereof, capable of increasing manufacturing yield by widening a range of gamma correction. An exemplary organic light emitting display includes a display region with pixels at crossings of data and scan lines; a gamma correction unit; a gamma correction circuit; a data driver; and a scan driver. The gamma correction unit includes first and second register units for storing first and second gamma correction signals, the second gamma correction signal comprising a corrected first gamma correction signal; a booster unit for correcting the second gamma correction signal to generate a third gamma correction signal; and a multiplexer for selecting the second gamma correction signal or the third gamma correction signal outputted from the booster unit, and for transferring it to the gamma correction circuit.