Direct electron transfer of horseradish peroxidase, immobilized on a functional membrane-modified gold electrode, was studied. The electrode showed a quasi-reversible electrochemical redox behavior with a formal potential of 60mV (versus Ag/AgCl) in 20mM potassium phosphate buffer solution at pH 7.0 and temperature 25°C. The cathodic transfer coefficient was 0.42 and electron transfer rate constant was evaluated to be 1.6s⁻¹. Furthermore, the modified electrode was used as a biosensor and exhibited a satisfactory stability and sensitivity to H₂O₂. The linear range of this biosensor for H₂O₂ determination was from 5.0×10⁻⁶ to 1.5×10⁻⁴M while its detection limit, based on a signal-to-noise ratio of 3, was 1.3×10⁻⁶M. The apparent Michaelis–Menten constant (K_m^app) for immobilized HRP was calculated to be 1.6×10⁻⁴M.