Provided is a method of fabricating an organic light emitting device using a solution process. The method includes forming an electrode on a lower substrate; depositing an organic active material solution containing at least one photoreactive material on the electrode to form an organic active material layer; and radiating light onto the organic active material layer so that a characteristic of the light varies according to the depth of the organic active material layer in order to gradually vary a molecular orientation structure in the organic active material layer according to the depths, thereby resulting in a carrier mobility gradient according to the depths of the organic active material layer.