PROBLEM TO BE SOLVED: To provide: an oxidant solution for production of conductive polymer which enables the production of a solid electrolytic capacitor having a high voltage resistance; a solid electrolytic capacitor produced by use of such an oxidant solution; and a method for production thereof.SOLUTION: An oxidant solution comprises an organic ferric sulfonate as an oxidant. The organic ferric sulfonate includes an organic sulfonic acid which includes an alkylbenzene sulfonic acid expressed by the general formula (1), and a benzene sulfonic acid which are combined in a particular proportion in quantity. The oxidant solution is used to form a conductive polymer, whereby a solid electrolytic capacitor having a high voltage resistance can be obtained. Further, a method for manufacturing the solid electrolytic capacitor is provided.
