An organic light emitting display includes pixels positioned at intersections between data lines and scan lines, a data change unit receiving first data of i (i is a natural number) bits to generate second data of j (j is a natural number equal to or larger than i) bits so that a desired gamma value is realized, a gamma voltage unit for generating gray scale voltages corresponding to l (l is a natural number larger than i) bits, and a data driver for selecting one of the gray scale voltages as a data signal to correspond to the second data and for supplying the data signal to the data line.