To provide a method of efficiently manufacturing a solid electrolytic capacitor which is capable of effectively restraining a leakage current from leaking out, when operating on a high voltage and superior in quality.

The method of manufacturing a solid electrolytic capacitor comprises processes of forming an oxide film on a metal material having valve action, applying a solution which contains conductive polymer forming monomer and another solution which contains an oxidant repeatedly and alternately on the oxide film formed on the metal material, and polymerizing the monomer into a conductive polymer. In this manufacturing method, the valve action metal material is used, on which the oxide film of thickness 30 nm or larger has been formed, and the monomer is polymerized into the conductive polymer, under the conditions that humidity be over 15% RH and below 45%, and the temperatures are kept at 10°C to 60°C in the atmosphere.