Poly(aniline-co-o-aminophenol) (PAN–OAP) has been synthesized by electrochemical copolymerization of aniline (AN) and o-aminophenol (OAP) on glassy carbon electrode (GCE). FT-IR, UV–vis and electrochemical characterizations indicate the formation of the PAN–OAP and it has the structure of a head-to-tail coupling of AN and OAP units. When the concentration ratio of OAP–AN is more than 1:20, the voltammetric behaviors for the copolymerization of AN and OAP are similar, while the copolymerization rate decreases with increasing of OAP concentration in the solution. The PAN–OAP can maintain its electroactivity in neutral and even in alkaline media, although the electroactivity of the copolymers decrease with increasing of the concentration ratio of OAP–AN in solution. The PAN–OAP film coated GCE exhibits excellent electrocatalytic responses towards the electro-oxidation of ascorbic acid (AA) in phosphate buffer solution of pH 6.8. The anode peak potential of AA shifts from 0.53V at bare GCE to 0.21V at PAN–OAP/GCE with greatly enhanced current response. A linear calibration graph is obtained over the AA concentration range of 5×10−4–1.65×10−2 molL−1 using cyclic voltammetry. Chronoamperometry has also been employed to investigate the electro-oxidation of AA. The PAN–OAP/GCE shows good stability and reproducibility.