The oxidation-reduction properties,relative to the Fe(Ⅲ)/Fe(Ⅱ) conversion,of horseradish peroxidase(HRP)in surfactant films at edge-plane pyrolytic graphite(EPG)electrode have been investigated by using direct electrochemical methods.Cyclic voltammograms for DDAB/HRP/CME(chemically modified eelctrode),DMPC/HRP/CME,DHP/HRP/CME at 2V/s in phosnhate buffer solution (pH 7.O) show one pair of reversible,reproducible redox peaks. The redox potentials (E1/2) in DDAB/HRP/CME,DMPC/HRP/CME and DHP/HRP/CME are-0.212V,-0.330V,-0.381V respectively. Experimental result indicated that the membranes,especially the positively charged one,providing special film environment,might interfere in the protein-electrode electron transfer process. The electron transfer processes of HRP were described in the absence and in the presence of hydrogen peroxide.There are good linear relationships between the currents and the H2 O2 concentration using all the three CMEs.The results obtained are of potential value for basic and applied bioelectrochemistry and represent an opportunity to build the third generation of biosensors.