Disclosed is a method of manufacturing an organic light emitting device, which comprises the steps of successively stacking a bottom electrode, an organic layer including an emission layer, and a top electrode, the method further comprising the step of: surface-treating the bottom electrode with ion beam etching before stacking the organic layer. By effectively removing impurities such as polymer materials or oxidation films, which are formed on the bottom electrode of the organic light emitting device, not only electron injection and hole injection in the organic light emitting device progress smoothly, but also an operation voltage is lowered and performance reliability can ensured because the surface roughness of the bottom electrode is maintained at the same level before and after ion milling.