The adsorption of Immunoglobulin G on a titanium dioxide (TiO2) electrode surface was investigated using I-125 radiolabeling and electrochemical impedance spectroscopy (EIS). I-125 radiolabeling was used to determine the extent of protein adsorption, while EIS was used to ascertain the effect of the adsorbed protein layer on the electrode double layer capacitance and electron transfer between the TiO2 electrode and the electrolyte. The adsorbed amounts of Ig.G agreed well with previous results and showed approximately monolayer coverage. The amount of adsorbed protein increased when a positive potential was applied to the electrode, while the application of a negative potential resulted in a decrease. Exposure to solutions of Ig.G resulted in a decrease of the double layer capacitance (C) and an increase in the charge-transfer resistance (R-2) at the electrode solution interface. As more Ig.G adsorbed onto the electrode surface, the extent of C and R-2 variation increased. These capacitance and charge-transfer resistance variations were attributed to the formation of a proteinaceous layer on the electrode surface during exposure.