A stable electroactive thin film of poly(azure I) (PAI) was deposited on the surface of a glassy carbon electrode by cyclic voltammetry from azure I (AI) in an aqueous solution. Cyclic voltammograms of PAI indicate the presence of two redox couples and the formal potentials of both shift Linearly towards the negative direction with increasing solution pH. The PAI-modified glassy carbon electrode shows excellent electrocatalytic activity toward NADH oxidation in phosphate buffer solution (pH 7.0), with an overpotential of more than 460 mV lower than that of the bare electrode. The catalytic rate constant of the modified glassy carbon electrode for the oxidation of NADH is determined by cyclic voltammetry and rotating disk electrode measurements.