The passivation and anodic oxidation of duplex TiN coatings deposited by are ion plating onto prenitrided AISI 304 stainless steel have been studied by potentiodynamic polarization, electrochemical impedance spectroscopy, and Mott-Schottky measurements in 0.1 M H2SO4 + 0.05 M HCl. The chemical composition of the oxidized surface film atop TiN was analyzed by X-ray photoelectron spectroscopy. Up to 1.2 V/SHE the TiN coating exhibits passive behavior, which is attributed to the formation of a TiO2-like film of nanometer thickness which grows linearly with anodic potential at a rate of 2.4 nm/V, Above 1.2 V/SHE enhanced anodic oxidation of TiN is observed at a rate of 17.7 nmN, and the overall corrosion performance is governed both by the oxidized TiN coating and by a metallic Ti interlayer atop the nitrided stainless steel substrate. At all potentials the TiO2 film is characterized by relatively high donor densities and is, furthermore, terminated by a hydroxylated surface.