In this work, various Ti-Si-N coating layers, composites of TiN crystallites and amorphous Si3N4, where free Si existed depending on the amount of total Si content in Ti-Si-N film, were prepared on Si substrates by a d.c. reactive magnetron sputtering method in order to systematically investigate the effects of Si contents and free Si on the oxidation behavior. The oxidation process at 800 degreesC started by forming thin oxide layer of ternary Ti-Si-O at the interface, and the ternary Ti-Si-O layer was segregated into two phases of TiO2 and SiO2. Oxidation resistance of Ti-Si-N coating layers was significantly improved with increasing Si contents, which resulted in the increase of SiO2 amount acting as an oxygen diffusion barrier. Free Si was diffused and segregated toward surface region, while Si bonded to nitrogen in Si3N4 could not. The free Si in Ti-Si-N coating layers was believed to partly contribute to the much enhanced oxidation resistance. (C) 2003 Elsevier B.V. All rights reserved.