Electrochemical polymerization of poly(3-methyl thiophene) films (3-MTy) which are self-doped with SO3- was investigated. The sulfonated poly(3-methyl thiophene) films synthesized from the solution which contained different amounts of HSO3F. The sulfonated polymer films were found to be soluble in DMF and KOH. The solubility values increased and the conductivity values decreased with the increase in sulfonation ratio. The resulting polymers were characterized by cyclic voltammetry, UV-Vis, FT-IR, elemental analysis, dry conductivity measurements and SEM techniques. (C) 2004 Elsevier Ltd. All rights reserved.