A method of manufacturing an organic light-emitting display device is provided. The method includes: forming a lower electrode pattern on a substrate, which includes a transistor area and a capacitor area, to correspond to the transistor area and forming a buffer layer on the substrate including the lower electrode pattern; forming a thin-film transistor including an oxide semiconductor layer on the buffer layer; forming an interlayer insulating film on the thin-film transistor; forming a photoresist film pattern including first and second holes, which have different depths, on the interlayer insulating film; and forming a first contact hole, which exposes the lower electrode pattern, and second contact holes, which expose the oxide semiconductor layer, at the same time using the photoresist film pattern.