We have investigated the change in surface wettability of n-type semiconductor TiO2 electrode surfaces induced by cathodic polarization. While the wettability of polycrystalline anatase electrode surfaces did not change remarkably regardless of the electrode potential, the surface of amorphous TiO2 electrodes becarrie highly hydrophilic under cathodic conditions without UV light irradiation. We conclude that the increase in the number of hydroxyl groups due to electron addition to the near-band-edge trap sites accompanied by proton intercalation is responsible for the present hydrophilic conversion under cathodic conditions.