Electrocopolymerization of 3,4-ethylenedioxythiophene (EDOT) and 5-methylindole (5MeIn) was successfully carried out in acetonitrile containing lithium perchlorate as supporting electrolyte although the oxidation potentials of 5MeIn and EDOT were quite different. The influence of feed ratios and applied potentials on the copolymerization were investigated. The novel low band gap copolymers own both the advantages of P5MeIn and poly(3,4-ethylenedioxythiophene), i.e., good redox activity, good thermal stability, and high conductivity. The resulting copolymers were characterized by electrochemistry, FT-IR and ultra violet-visible spectroscopy, elemental analysis, thermal analysis, conductivity, and scanning electron microscopy, respectively.