Abstract: The solid electrolytic capacitor disclosed has an electron donor organic compound layer of an organic compound provided between an oxide film as a dielectric and a conductive polymer layer and a conductive polymer layer as a solid electrolyte layer. In the step of forming the electron donor organic compound layer, the pellet on which the oxide film is formed, is caused to be exposed to vapor of the electron donor organic compound, and this enables the formation of a thin and uniform electron donor organic compound layer on the oxide film irrespective of the kind of electron donor organic compound. The pellet may alternatively be dipped in a solution of the electron donor organic compound. Where the dipping process uses silane coupling agent, aluminum coupling agent or titanium coupling agent, the thin and uniform electron donor organic compound layer can be formed by using alcohol solution or acidic solution of each coupling agent.