A method of manufacturing an organic light-emitting display device is disclosed. The method includes: uniformly forming an active layer on an entire surface of a substrate on which an organic light-emitting diode, a thin film transistor (TFT), and a capacitor are to be formed; performing a first mask process on the active layer to form a pixel electrode of the organic light-emitting diode, a gate electrode of the TFT, and an upper electrode of the capacitor; performing a second mask process to form an insulating layer having openings that expose the pixel electrode, the upper electrode, and the active layer in a region of the TFT; performing a third mask process to form a source-drain electrode that contacts an exposed portion of the active layer; and performing a fourth mask process to form a pixel-defining layer (PDL) that exposes the pixel electrode and covers the TFT and the capacitor.