Coatings of Ti-Si-N on WC-Co substrates were deposited by an r.f. inductively coupled (RFl) PECVD technique. Ti-Si-N coating layers were grown with fairly high deposition rates, and had a maximum hardness value of 38-40 GPa when deposited at 500-600 degreesC with a Si content of approximately 10 at.%. The film microstructure of maximum hardness was revealed to be a nanocomposite of nano-sized TiN crystallites embedded in amorphous silicon nitride phase by high resolution transmission electron microscopy (HRTEM). The increase of Si content above 10 at.% caused thickening of amorphous silicon nitride phase and an appearance of free Si, although increasing Si also induced finer and more isotropic TiN crystallites with full percolation by amorphous phase. The deposition behaviors of Ti-Si-N, their microstructures, and mechanical property by an RFI-PECVD method were systematically investigated in this work.