Nano structured TiN coatings were prepared by means of active screen plasma nitriding (ASPN) method at a constant temperature of 550 °C for 5, 7.5 and 10 h under three gas mixtures of H2:N2% = 3:1, 1:1 and 1:3. In order to investigate the coating properties such as the chemical composition, surface morphology, surface topography and hardness, several analysis techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and nano indentation were employed. The results indicated that the growth of the TiN film under active screen plasma nitriding deposition had a (2 0 0) preferred orientation. Moreover, it was found that N2-50%H2 atmosphere provides the highest deposition rate leading to the maximum roughness and minimum nano hardness values. Similar observation was obtained by increasing the nitriding time. Furthermore, a model was proposed for the relation between the hardness and the surface roughness of the coating in which higher surface roughness leads to lower hardness.