Abstract: Nitrogen and Silicon co-incorporated DLC (N-Si-DLC) films were deposited by RF-CVD method. X-ray photoelectron spectrometer, Raman, surface profilometer and scanning electron microscope were used to characterize the structure and composition of the films. The humidity effect on the tribological properties of the films sliding against an 316L stainless steel ball was investigated by a ball-on-disk type reciprocating tribometer in humid air (relative humidity of 15%, 45% and 75%). The results show that the N-Si-DLC films possessed higher sp²C content and lower internal stress. The N species was attributed to C=N, C≡N, and Si-N. N-Si-DLC films with a small amount of N exhibited lower friction and wear compared to Si-DLC film. Also, these films showed low frictional sensitivity to the environmental humidity.