Hydrogen impermeability of TiN film and its dependence on film thickness has been investigated by the molten salt electrochemical technique. TiN films with different film thickness were prepared by cathodic arc ion plating. They were used as working electrodes, and cyclic voltammetry and potential-step chronoamperometry were conducted in LiCl-KCl-LiH melts at 723 K. Hydrogen diffusion coefficients through the TiN films were independent of film thickness, approximately 1.0 X 10(-7) cm(2) s(-1). By considering the results obtained from electrochemical investigations combined with surface analysis, the dependence of hydrogen impermeability on morphology of the film has been also examined.