The synthesis and electrochemical characterization of a new organic/inorganic hybrid material was performed by combining polypyrrole and a hexacyano metalate (nickel hexacyanoferrate (NiHCNFe)) aiming to obtain an electrocatalyst for H2O2 reduction in the presence of either Na+ or K+ ions. The use of this material as a redox mediator in an oxalate biosensor based on the immobilization of oxalate oxidase enzyme was also discussed. The electrochemical properties of the hybrid material were investigated by using impedance measurements and compared with those of the nickel hexacyanoferrate film alone. The electrocatalytic properties of the hybrid for reducing H2O2, in the presence of both Na+ and K+ ions, are higher than those of the NiHCNFe film due to the presence of polypyrrole chains that enhances the electronic conductivity of the material. (c) 2005 Elsevier B.V. All rights reserved.