Properties of the oxide layer formed on a TiN coating by anodic oxidation in neutral borate buffer solution were investigated using cyclic voltammetry, AFM, FT-IR, impedance and photocurrent measurements. The voltammogram showed imperfections in the TiN coating and high susceptibility of anodic oxidation. The result of FT-IR showed the composition of an oxide layer, similar to TiO2, including OH- or water. Both impedance and photocurrent results confirmed that the oxide film has n-type semiconductor properties. The oxide would contain defects acting as intergap states, resulting in low efficiency of photo-induced free-carrier generation. It seems that these defects have their origin in degradation of the protective property of a TiN coating under anodic polarization.