Sulfonated polythiophene films were synthesized from the acetonitrile solution which contained different amounts of anhydrous fluorosulfonic acid (FSO3H). Electrochemical oxidation of thiophene produced self-doped conducting polythiophene films which were soluble in DMSO and KOH. The solubility and conductivity properties of the polymer films were dependent on the degree of sulfonation (C/S ratio) value. The solubility values increased and conductivity values decreased with increasing degree of sulfonation (decreasing C/S ratio). The resulting polymer structures were characterized by cyclic voltammetry, UV-Vis, FT-IR, elemental analysis, dry conductivity, intrinsic viscosity measurement and thermal gravimetric analysis (TG). (C) 2003 Elsevier B.V. All rights reserved.