Thermal stability of tetrahedral amorphous carbon (ta-C) films is higher than that of hydrogenated amorphous carbon. This study investigates hydrogen content effects on thermal stability of diamond-like carbon (DLC) coatings using materials with two different hydrogen contents (H: 10.8 and 25.3 at.%) annealed in vacuum at up to 600 degrees C. Indentation measurements of the films showed decreased hardness of the films annealed at temperatures greater than 400 degrees C. Raman spectroscopy revealed D-band and G-band splitting at those temperatures for films with 25.3 at.% hydrogen content, Structural change with hydrogen effusion occurred ca. 440 degrees C in both hydrogen content films. Structural changes in 25.3 at.% hydrogenated films affected tribological properties, but 10.8 at.% of hydrogen content films showed only slight changes. (C) 2008 Elsevier B.V. All rights reserved.