In an organic light emitting display with a data integrated circuit using the same, a buffer circuit comprises: a first capacitor receiving gradation voltage through a first terminal; a first inverter having an input terminal connected to a second terminal of the first capacitor; a second capacitor having a first terminal connected to an output terminal of the first inverter; a second inverter having an input terminal connected to a second terminal of the second capacitor; a third capacitor having a first terminal connected to an output terminal of the second inverter; and a first transistor connected to a second terminal of the third capacitor and controlling current flowing from a first power source to a data line so as to supply the gradation voltage to the data line in correspondence to the voltage supplied by the third capacitor. With this configuration, the gradation voltage is supplied regardless of the threshold voltages of the transistors.