In a method of forming a conductive layer, a conductive layer formed using the method, an organic electroluminescent device including the conductive layer, and a method of manufacturing the organic electroluminescent device, the method of forming the conductive layer comprises: pre-treating a substrate in order to improve adhesive force; coating a mixture solution which contains a sulfonate-based catalyst and a solvent on the substrate, and then drying the coated product; and performing vapor-phase polymerization by contacting the substrate on which the catalyst is coated with monomers which make up a conductive polymer in a vapor phase. The conductive layer obtained using the method of forming a conductive layer has high conductivity, high transmittance with respect to light having a wavelength of 300 nm to 700 nm, uniform thickness, and thermal-chemical stability.