Electropolymerization of thiophene on Pt and indium tin oxide electrodes was investigated in moderately concentrated aqueous perchloric acid. The use of this medium increases the solubility of thiophene and lowers the oxidation potential of the monomer to about 0.9 V vs. SCE instead of 1.6 V found in acetonitrile. The polythiophene films synthesized by this technique are homogeneous and have properties very similar to films for-med in organic media. In particular, Fourier transform IR analysis showed that strictly alpha,alpha’-polythiophene chains are obtained with a degree of polymerization of about 40 and conductivities ranging between 0.1 and 1 S cm-1.