A method of measuring damage of an organic layer of a thin film encapsulation includes: preparing a thin film encapsulation structure in which an inorganic layer is stacked on an organic layer, in which a light-emitting material is mixed; irradiating light to the thin film encapsulation structure so that light is emitted from the light-emitting material, the intensity of light emitted from the light emitting material decreasing over time; detecting a light emission lifetime of the light emitted from the light emitting material; and determining a degree of damage to the organic layer based on the light emission lifetime. Accordingly, a degree of the damage to the organic layer due to plasma may be easily detected, and the damage to the organic layer may be minimized based on the detected degree of the damage by improving plasma process conditions for an operation of forming an inorganic layer.