The copolymerization of indole (In) and 3methylthiophene (3MeT) was successfully achieved electrochemically in boron trifluoride diethyl etherate (BFEE) by direct anodic oxidation of the monomer mixtures on stainless steel electrodes although their respective oxidation potentials were quite different. The electrochemical properties of the copolymers were studied by cyclic voltammetry. Asformed free-standing insoluble copolymers owned both the advantages of polyindole (Pln) and poly(3-methylthiophene) (P3MeT), i.e., good thermal stability, good electrochemical activity, and high conductivity. The insert of 3MeT units in PIn was helpful to improve the conductivity of Pln and the insert of In units in P3MeT was also beneficial to improve the electrochemical and thermal stability of P3MeT. The influence of applied polymerization potential on the synthesis of copolymer was investigated. The higher potential favored the incorporation of 3MeT units into the copolymers. 1.3 V vs. SCE was tested to be the best potential for the electrochemical copolymerization of In and 3MeT. The structure and morphology of the copolymers were investigated by UV-vis spectroscopy, infrared spectroscopy, thermal analysis, and scanning electron microscopy (SEM), respectively. Polymerization mechanism studies showed that the polymerization of indole ring occurred at 2,3 position. (c) 2007 Wiley Periodicals, Inc.