An organic light emitting display can include a display panel including a plurality of pixels of a source following manner, in which a source voltage of a driving thin film transistor (TFT) is changed according to a current flowing between a drain electrode and a source electrode of the driving TFT, a gate driving circuit for generating a mobility sensing gate pulse for operating the pixel in the source following manner, a data driving circuit for detecting a sensing voltage corresponding to mobility of the driving TFT from the pixel in response to the mobility sensing gate pulse, and a timing controller for setting a mobility sensing period in a period, in which a gate-source voltage of the driving TFT is greater than a threshold voltage of the driving TFT.