The glassy carbon electrode (gce) and highly oriented pyrolytic graphite (hopg) were electrochemically anodized at a potential of +2.0 V (vs. Ag/AgCl) to create active sites and to improve the adsorption of glucose oxidase (GOD) and flavin adenine dinucleotide (FAD) on the electrode surfaces. The GOD and FAD irreversibly adsorbed onto the anodized electrodes to form very stable modified surfaces. Direct electron-transfer reaction takes place between the adsorbed GOD and the anodized electrodes, but the adsorbed enzyme cannot catalyze its substrate to oxidize due to its denaturation. Two possible denatured processes have been proposed. Based on the analyses of scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscope (STM), it is confirmed that the adsorbed GOD molecules extend to the unfolded structure owing to strong interaction between the enzyme and the electrode surface, but the FAD redox centers of the enzyme do not divorce from the apoenzyme.