Disclosed is a method of manufacturing a surface-modified polymer film, including forming a hydroxyl group (—OH) on the surface of a polymer film by subjecting the polymer film to light irradiation and surface treatment with a photoacid generator. The polymer film can be introduced with a hydroxyl group (—OH) group using a photoacid generator, thereby modifying the surface of the polymer film without damage to the polymer film. Also, an organic electronic device including the surface-modified polymer film can be improved in electrical characteristics and stability.