The invention provides a process for producing solid electrolyte capacitors by forming a dielectric oxide film and a first cathode layer of solid conductive substance over the surface of an anode body of valve metal, and forming a second cathode layer of conductive high polymer on the first cathode layer by electrolytic oxidative polymerization. In forming the second cathode layer, the pH of the electrolyte to be used for electrolytic oxidative polymerization is maintained within a predetermined range by adding an acid or alkali to the electrolyte. Since the pH of the electrolyte remains substantially unaltered by the polymerization according to the invention, the electrolyte is repeatedly usable while permitting the resulting second cathode layers to retain the desired electric conductivity. The second cathode layer is formed by immersing in the electrolyte the anode body formed over the surface thereof with the oxide film and the first cathode layer, feeding a positive voltage with an external electrode piece in contact with the first cathode layer in the electrolyte, and shifting the feeding point at a predetermined time interval. The feeding point where the electrode piece is in contact with the first cathode layer for feeding shifts during the step of electrolytic oxidative polymerization, so that the thickness of the second cathode layer formed as centered about the feeding point is made uniform to the greatest possible extent over the entire anode body without increasing locally.