Copolymers of aniline and N-(3-sulfopropyl)aniline (NSPA) were electrosynthesized by a potential cycling procedure. The rate of electropolymerization increased with a larger aniline molar fraction in the electrolyte solution containing both monomers and with extending the upper potential limit to higher values. Electrochemical properties of the obtained copolymers depended on aniline and NSPA concentration ratio. The "first cycle effect", ie an increased anodic peak in the first potential scan, was shown to be suppressed in the copolymer, compared with polyaniline. This difference is discussed in terms of an inner anion doping process in the copolymer, which contains anionogenic sulphonate groups.