Copolymerization of aniline and p-aminophenol in aqueous sulfuric acid solutions was electrochemically performed using cyclic voltammetry on platinum electrodes. The monomer concentration ratio can strongly affect the copolymerization rate and electrochemical property of the copolymer. The optimum conditions for the copolymerization are that the potential sweep covers the -0.20 to 0.95 V (vs. SCE) potential range, and that a solution contains 0.18 M aniline, 0.02 M p-aminophenol and 0.50 M H2SO4. A resulting copolymer synthesized under the optimum conditions has a good electrochemical activity in 0.50 M solutions of Na2SO4 with pH <= 10.0. IR and XPS spectra indicate that -OH groups and SO42- ions are contained in the resulting copolymer. The SEM images reveal that the microstructure of the copolymer depends on the monomer concentration ratio during the electrolysis. (C) 2007 Elsevier Ltd. All rights reserved.