Electrochemical copolymerization of 3-methylpyrrole and N-methylpyrrole perchlorate doped has been carried out at two overpotentials and at different electrodeposition times in acetonitrile medium. A mixture of instantaneous and progressive nucleation mechanisms has been established from the current density-time transients. Doping/dedoping reversibility is deduced from the electrochemical study of copolymer films by cyclic voltammetry. Fourier Transform Infrared spectrum analysis shows that electropolymerization time has a great influence on the random monomers proportion in the copolymer obtained. Although the copolymer conductivity is in the range of the measured for poly 3-methylpyrrole and poly N-methylpyrrole obtained in similar conditions, it remains conductive for a much longer time than the homopolymers. (C) 2007 Elsevier B.V. All rights reserved.