NOVELTY - A conductive polymer has repeating unit (I). The area ratio of region having molecular weight of more than 5000 Da based on sodium polystyrene sulfonate conversion and region having molecular weight of less than 5000 Da based on sodium polystyrene sulfonate conversion is 0.6 or less, which is calculated by forming chromatogram of testing liquid using polymeric-material evaluation apparatus provided with gel-permeation chromatograph and then adjusting the holding time. The testing liquid is obtained by dissolving polymeric material in eluting solvent.    USE - Conductive polymer e.g. doped polyaniline. Uses include but are not limited to electrode of electrical double layer capacitor, additive of carbon layer of functional-polymer capacitor, electrodeposition coating material, transparent conductive resin board, film for overhead projectors, transparent conductive film for audio tape, antistatic agent of acidic dyeable fiber, electroluminescent display, counter electrode of di-sensitized solar cell, negative electrode material, etc.    ADVANTAGE - The conductive polymer has high electroconductivity and solubility, and does not generate foreign material.    DETAILED DESCRIPTION - A conductive polymer has repeating unit of formula (I). The area ratio of region having molecular weight of more than 5000 Da based on sodium polystyrene sulfonate conversion and region having molecular weight of less than 5000 Da based on sodium polystyrene sulfonate conversion is 0.6 or less, which is calculated by forming chromatogram of testing liquid using polymeric-material evaluation apparatus provided with gel-permeation chromatograph and then adjusting the holding time. The testing liquid is obtained by dissolving polymeric material in eluting solvent such that the pH of the resultant mixture is 10 or more and solid concentration is 0.1 %mass.    R1-R4=H, 1-24C linear or branched alkyl, 1-24C linear or branched alkoxy, acidic group, hydroxy, nitro, -F, -Cl, -Br or -I, where at least one of R1-R4 is acidic group or its salt.    INDEPENDENT CLAIMS are included for the following:    (1) quality control method of conductive polymer; and    (2) purification of conductive polymer, which involves membrane-filtrating conductive polymer, dissolving filtered conductive polymer in a solvent, and contacting solvent containing conductive polymer with strongly basic anion-exchange resin and carbon material.