A method of detecting a defect in an organic light-emitting display device includes: preparing an organic light-emitting display device including an organic light-emitting display panel which includes a plurality of pixels, where each of the pixels includes a driving transistor which operates in a saturation region or a transition region based on a potential difference between a source and a drain thereof and outputs a driving current, and an organic light-emitting diode which emits light based on the driving current; providing a plurality of voltages to the organic light-emitting display panel to operate the driving transistor in the transition region, and determining whether the organic light-emitting display device is defective based on an image, which is displayed on the organic light-emitting display panel based on data applied thereto.