Titanium nitride (TiN) coatings with a dense structure were prepared on high-speed steel by plasma-assisted chemical vapour deposition (PACVD). The electrochemical polarization measurement of TiN coating was compared with that of the uncoated substrate. It was found that the TIN coating had a higher corrosion potential, and a lower corrosion rate (current density), about three orders of magnitude less than for the steel substrate. The major corrosion mechanism of TiN was pitting corrosion through surface defects and/or open pores. The number and size of pits decreased with the chlorine content of the film. The TiN coating deposited by PACVD, regardless of the amount of residual chlorine, proved to be a good anticorrosion coating on a steel substrate.