Pt-containing polythiophenes were obtained by two different methods: (i) treatment of preformed polythiophene with an aqueous solution containing Pt(II) ions, and (ii) the polymerization of 2,2′-bithiophene in a solution of acetonitrile containing Pt(II) ions. The X-ray photoelectron spectra of these Pt-containing polymers suggested that Pt was in the Pt(II) state; the electrical conductivity was 0.027 - 0.6 S cm-1at 300 K with an activation energy of 80 - 118 meV, depending on the method of preparation. The cyclic voltammogram of a perchlorate film pretreated with a Pt solution showed a well-defined anodic-current peak at 0.59 V versus Ag/AgCl and a cathodic-current peak at -0.26 V in an aqueous system. The observed negative reduction potential indicated that the polythiophene electrode became electrochemically resistant to protic solvents by Pt complexation. © 1989.