TiN thin film has been produced on the surface of AISI D6 tool steel by using a titanium interlayer. In this work, the morphology, the microstructure and interface depth profile of TiN films deposited at two substrate temperatures (220 T and 450 degrees C) in the coating process are presented and discussed. The AISI D6 tool steel substrates were coated with titanium thin film as the underlayer and with TiN thin film as the top layer. They were deposited by conventional cathodic arc process. The surfaces of TiN films were observed by scanning electron microscopy (SEM). The microstructure of these samples was analysed by X-ray diffractometry (XRD). The influence of the substrate temperature on the TiN film-Ti film-AISI D6 interface region were investigated by energy dispersive spectrometry (EDS) and its cross section were observed using backscattered electron image (BEI). The results showed that TiN films deposited at 220 degrees C formed a film of strongly (111) preferred orientation, while in 450 degrees C formed a film of (111) and (220) preferred orientation. The thickness of the TiN films increased with increasing substrate temperature. The results show that the interface region of the TiN film-Ti film-AISI D6 substrate system was significantly improved when higher substrate temperature during deposition is used.