Composite SiN x /DLC films were deposited on Si substrate by RF magnetron sputtering of silicon nitride (Si 3 N 4 ) target simultaneously with filtered cathode arc (FCA) of graphite. The RF power was fixed at 100 W whereas the arc currents of FCA were 20, 40, 60 and 80 A. The effects of arc current on the structure, surface roughness, density and mechanical properties of SiN x /DLC films were investigated. The results show that the arc current in the studied range has effect on the structure, surface roughness, density and mechanical properties of composite SiN x /DLC films. The composite SiN x /DLC films show the sp 3 content between 53.5% and 66.7%, density between 2.54 and 2.98 g/cm 3 , stress between 1.7 and 2.2 GPa, and hardness between 35 and 51 GPa. Furthermore, it was found that the density, stress and hardness correlate linearly with the sp 3 content for composite SiN x /DLC films.