An organic light emitting display includes a display panel, a power supply circuit, a voltage detection unit and a voltage compensation unit. The display panel includes a plurality of pixels. The power supply circuit outputs a first power source to the display panel. The voltage detection unit is positioned between the display panel and the power supply circuit, and detects a detection voltage data of the first power source output from the power supply circuit. The voltage compensation unit compares the detection voltage data with a previously stored reference voltage data, and controls the power supply circuit to output the first power source having a voltage level set based on the reference voltage data.