Copolymerization of 2,5-diaminobenzenesulfonic acid (DABSA) and para-phenylenediamine (PPDA) respectively, with aniline (AN) was electrochemically performed by cyclic voltammetry on IrO2-coated electrodes in 1 M HCl. The copolymerization rate strongly depends on the amount of DABSA/PPDA in the comonomer feed. The composition analysis results indicate that the cross-linking and branching reactions occur simultaneously during copolymerization at the fraction of DABSA larger than 0.206 in DABSA-AN comonomer feed. The above mentioned two reactions exist in the PPDA-AN copolymerization system at PPDA levels of 0.102 in comonomer feed. From x-ray photoelectron spectroscopy results, the C-1s lines show that the net charge residing on the carbon atoms is affected neither by reaction time (cycle number) nor by the DABSA/PPDA fraction in the feed. The N-1s lines show that the second component peak corresonding to an amine site at 400.4 eV is more dominant for both DABSA and PPDA-modified polyanilines. The composite film of DABSA/PPDA-AN copolymer with waterborne polyurethane was prepared, and its conductivity measured to compare the effect of DABSA/PPDA in the comonomer feed. Stability testing shows DABSA-AN copolymer film more stable than PPDA-AN copolymer film. Electrochemical response of the modified polyanilane films to dissolved hydroquinone and Fe(CN)(6)(-4) was also examined.