Ti-Si-N coating layers were codeposited on silicon wafer substrates by a DC reactive magnetron sputtering technique using separate titanium and silicon targets in $N_2$/Ar gas mixtures. The oxidation behavior of Ti-Si-N coating layers containing 4.0 at.%, 10.0 at.%, and 27.3 at.% Si was investigated at temperatures ranging from 600 to $960^{circ}C$. The coating layers containing 4.0 at.% Si became fast oxidized from $600^{circ}C$ while the coating layers containing 10.0 at.% Si had oxidation resistance up to $800^{circ}C$. It was concluded that an increase in Si content to a level of 10.0 at.% led to the formation of finer TiN grains and a uniformly distributed amorphous Si3N4 phase along grain boundaries, which acted as efficient diffusion barriers against oxidation. However, the coating layers containing 27.3 at.% Si showed relatively low oxidation resistance compared with those containing 10.0 at.% Si. This phenomenon would be explained by the existence of free Si which was not nitrified in the coating layers containing 27.3 at.% Si.