A solid electrolytic capacitor includes: a dielectric oxide film 2; a solid electrolyte 3 composed of a conductive polymer; a carbon layer 4; and a silver layer 5; formed sequentially on a surface of an anode 1 composed of a valve metal. The capacitor has excellent leakage current characteristics and electrical characteristics under hot and humid conditions due to doped naphthalenesulfonic acid compounds in the conductive polymer.