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Copper-mediated graft-copolymerization of methyl methacrylate (MMA) onto casein was studied in this paper. The casein-g-PMMA was isolated by solvent extraction and was identified by Fourier transform infrared spectra (FTIR). Transmission electron microscope (TEM) micrographs revealed the presence of core-shell particles where PMMA was the core and casein was the shell. A glucose oxidase electrode with immobilizing carriers of casein-g-PMMA and polypyrrole membrane was prepared by a multiple-step electrochemically polymerization. The effects of reaction conditions such as working voltage, glucose concentration, temperature and solution pH on the characteristics of electrode bioelectrochemical response were discussed. The sensitivity and stability of the electrode were also investigated. Experimental results showed that the multiple enzyme electrode's linear range was 1.0 times 10-6~ 1.43 times 10-2 mol/L and the detection limit was 1.0 times 10-7mol/L, the stable response time was 8 seconds. The electrode exhibited favorable repeatability and selectability, and its lifetime was greater than one month. The glucose biosensor will have a widest application in clinical diagnosis.