Novel enzyme-free and direct electrochemical glucose biosensors, using glassy carbon electrode modified by iron oxide nanoparticles-decorated MWCNTs are fabricated. The MWCNTs were synthesized by catalytic chemical vapor deposition using ferrocene as a floating catalyst and functionalized in HNO3. The morphology and structure of the samples were characterized with transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared (FTIR). The electrocatalytic activity of the modified electrode toward glucose oxidation was evaluated by cyclic voltammetery and amprometry in 0.05 M phosphate buffer solution at pH 7.0. The results show that the functionalized MWCNTs significantly enhance the catalytic behavior of Fe3O4 for glucose oxidation. The direct electron transfer coefficient between the electrode surface and glucose is 0.35. The prepared electrode shows a linear behavior in the range of 0.5-7.0 mM with a high sensitivity of 238.7 mu A mM(-1) cm(-2) and a low detection limit of 15.0 mu M at S/N = 3.0. The glucose biosensor exhibits reproducible response, long-term stability, as well as no interference from ascorbic and uric acids. (C) 2013 The Electrochemical Society.