Mo-Al-Si-N films were deposited by direct current magnetron sputtering using different nitrogen flow rates. The structure and mechanical properties of these films were investigated by means of X-ray diffraction, field emission scanning electron microscopy, field emission electron probe microanalysis and nanoindentation. The results indicate that the deposition rate decreases from 24.5 to 11.8 nm/min with increasing nitrogen flow rate from 7.5 to 30 sccm, while the grain size of films decreases firstly from about 24 to 14 nm and then increases to about 25 nm. The preferred orientation of the Mo-Al-Si-N films changes from (111) to (200) due to the increase of surface energy and the decrease of strain energy. The lattice parameter increases from 4.177to 4.186 angstrom due to the excess nitrogen atoms occupying interstitial positions of Mo-Al-Si-N films. It is worthy to note that Mo-Al-Si-N films deposited using a nitrogen flow rate of 15 sccm display higher hardness and better toughness, which are mainly determined by the grain size. (C) 2015 Elsevier B.V. All rights reserved.