Poly(o-phenylenediamine-co-o-aminophenol) (PoPDoAP) was firstly synthesized via the electrochemical copolymerization of o-phenylenediamine (o-PD) and o-aminophenol (o-AP) in aqueous H2SO4 solution. The monomer concentration ratio strongly affected the electrochemical properties of the copolymer. The results from electrochemical impedance spectroscopy (EIS) indicated a copolymerization reaction took place between o-PD and o-AP. Compared to poly(o-phenylenediamine) (PoPD), the copolymer exhibited novel and improved electrical properties. The effect of the scan rate on the redox activity was also studied, indicating the electrochemical process of the copolymer is diffusion-controlled. A possible copolymerization mechanism was deduced from the IR spectrum of the copolymer. (C) 2013 The Electrochemical Society. All rights reserved.