In this work, the magnetic core-shell Fe(3)O(4)@Au nanoparticles attached to the surface of a magnetic glassy carbon electrode (MGCE) were applied to the immobilization/adsorption of myoglobin (Mb) for fabricating Mb/Fe(3)O(4)@Au biofilm. The morphology, structure, and electrochemistry of the nanocomposite were characterized by transmission electron microscope, UV-vis spectroscopy, electrochemical impedance spectroscopy, and cyclic voltammetry, respectively. The resultant Fe(3)O(4)@Au NPs not only have the magnetism of Fe(3)O(4) NPs that make them easily manipulated by an external magnetic field, but also have the good conductivity and excellent biocompatibility of Au layer which can maintain the bioactivity and facilitate the direct electrochemistry of Mb in the biofilm. The modified electrode based on this Mb/Fe(3)O(4)@Au biofilm displayed good electrocatalytic activity to the reduction of H(2)O(2) with a linear range from 1.28 to 283 microM. The proposed method simplified the immobilization methodology of proteins and showed potential application for fabricating novel biosensors and bioelectronic devices.