The electrochemical copolymerization of diphenylamine(DPA) and o-aminophenol(OAP) was studied by using in situ ultraviolet-visible(UV-Vis) spectroelectrochemical and cyclic voltammetric techniques.The different voltammetric characteristics between the homopolymerization and copolymerization processes exhibited the occurrence of the copolymerization of DPA and OAP in 4 mol/L H2SO4.The in situ UV-Vis spectra showed that,during the copolymerization of DPA and OAP,DPA and OAP were firstly oxidized to generate their cation radicals，then a mixed oligomer intermediate was formed by the cross-reaction of the cation radicals of DPA and OAP with the DPA and OAP monomers or their cation radicals in solution,and the absorption peak located at 508 nm was assigned to this intermediate.Further studies showed the difference was existed between the copolymerization of DPA and OAP with different concentration ratios,indicating the dependence of the copolymerization on the concentrations of DPA and OAP.