Diamond-like nanocomposite (DLN) is a class of modified diamond-like carbon (DLC) coatings. The DLN films consist of amorphous networks of carbon and silicon, which are made by incorporating the Si-O structures into the DLC films. The thermal stability of DLN films was investigated by annealing the films deposited on Si (1 0 0) substrates by plasma enhanced chemical vapor deposition. The films were heated in ambient air for 1 h at the annealing temperatures ranging from 200 to 600 degreesC. The mechanical properties as well as structural modification of the annealed films were investigated as a function of annealing temperature. The chemical structure, composition, thickness and hardness values of the annealed films were measured by Raman spectrometer, electron probe micro analyzer, scanning electron microscope and ultra micro-indentation system, respectively. The comparison between DLN and DLC films on their thermal stability was made in order to understand the characteristics of DLN films. It is assumed that the DLN films show a good thermal stability for the protective coating applications at high temperature environment in air atmosphere in comparison with DLC films. (C) 2003 Elsevier Science B.V. All rights reserved.