Abstract: A hemoglobin/poly (L-glutamic acid)/glassy carbon electrode (Hb/PGA/GCE),targeted for reversible oxidation of p-phenylenediamine(PPD),has been fabricated by covalently immobilizing Hb on GCE with a thin layer of conductive pre-electropolymerized PGA.Electrochemical impedance spectra of the electrode confirmed the immobilization of Hb.The resulting modified electrode(Hb/PGA/GCE) gave a redox couple for Hb in PBS buffer and a better electrocatalytic performance to H₂O₂.This indicated that the direct electron transfer of the active group of the protein could be retained on the electrode surface.The oxidation of PPD was reversible on Hb/PGA/GCE instead of GCE or PGA/GCE.The redox peak current was proportional to the scan rate,and I_p,a/I_p,c about 1.02,indicating a characteristic of quasi-reversible,surface confined electrochemical behavior.Moreover,a new measurement method for PPD in samples was provided since the redox peak currents increased linearly with the concentration of PPD,I_p,a (μA)=3.124+0.705 c_PPD (mmol/L) (r=0.9973).The enzymatic oxidation might be the plausible mechanism because the existence of H₂O₂ was in favor of the reversible redox of PPD.