The invention provides an electroconductive-polymer solution with which a capacitor having a high capacitance, a low ESR, and excellent long-term reliability can be formed without requiring the use oftreating liquids for electroconductive-polymer layer formation which differ in makeup or without forming any inner electroconductive-polymer layer by a different means; the capacitor; and a process for producing the capacitor. The present invention relates to: an electroconductive-polymer solution, a capacitor which includes either the electroconductive-polymer solution or the compounds remainingafter removal of the solvent from the solution; and a process for capacitor production which includes impregnating the capacitor with the electroconductive-polymer solution and removing the solvent therefrom, wherein the electroconductive-polymer solution comprises an electroconductive polymer and a solvent, the electroconductive polymer comprises a [pi]-conjugated electroconductive polymer, a polyanion with which the [pi]-conjugated electroconductive polymer has been doped, and a compound formed by reacting an oxirane or oxetane group with an anion moiety of the polyanion which makes no contribution to the doping, and the solution has a pH of 2.0-6.0.