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A feasible and fast method for glucose oxidase (GOx) study was developed by covalent attachment of GOx to gold-coated magnetic iron oxide nanoparticles (Fe@Au).GOx molecules were oxidized with metaperiodate to form aldehyde group. The prepared Fe@Au composite nanoparticles with 60 nm diameter were used as a carrier for the immobilization of GOx. Fe@Au nanoparticles were modified by cysteamine to produce amine groups at the surface. The GOx was covalently attached to the amine-modified Fe@Au nanoparticles through its aldehyde groups. The direct electrochemistry of GOx showed a quasi-reversible cyclic voltammogram corresponding to the flavin adenine dinucleotide (FAD/FAD[H.sub.2]) redox couple with a formal potential of -270 mV in 0.1 M phosphate buffer. The apparent charge transfer rate constant ([k.sub.s]) and transfer coefficient for electron transfer between the electrode surface and enzyme were calculated as 2.23 [s.sup.-1] and 0.45, respectively. The linear concentration range of the biosensor is 2.4-54 mM with detection limit of 0.51 mM at S/N = 3. The apparent Michaelis-Menten constant was measured to be 8.59 mM, indicating that the immobilized GOx on Fe@Au preserved its native activity. The life time of biosensor is more than 2 weeks. Keywords: biosensor, direct electrochemistry, glucose oxidase, gold-coated iron oxide nanoparticles, immobilization DOI: 10.1134/S1061934815100123, The determination of glucose concentration is very important in clinical, biological and chemical samples, as well as food processing and fermentation [1]. Chiefly glucose sensors have been studied most extensively [...]