The electrochemistry of microperoxidase-11 (MP- 11) was studied by cyclic voltammetry at a glassy carbon electrode modified with multi-walled carbon nanotubes (MWNTs). Further research indicates that MWNTs have promotional effects on the direct electron transfer between MP-11 and the surface of the MWNTs. The resulting electrodes showed a pair of well-defined redox peaks with a formal potential at about -0.26 V (vs. AgjAgCl) in phosphate buffer solution (pH 7.0). The electrochemical parameters, such as the apparent heterogeneous electron-transfer rate constant, were estimated. The experimental results also demonstrated that the immobilized MP-11 retained its bioelectrocatalytic activity to the reduction of H2O2 and O-2. The modified electrode could be used in biofuel cells. (c) 2005 Elsevier B.V. All rights reserved.