Abstract: a-Si:C films as protective coating have been attracting more and more attentions due to prominent characteristic such as good thermal stability, excellent wear resistant and corrosion resistant. For the different sliding parts applications, a-Si:C films often subjected to localized heating caused by friction in ambient air. Thus, it is interesting to study these films’ thermal stability and the mechanism of the low friction coefficient. Here, a-Si:C films were deposited by pulsed reactive magnetron sputtering in a gas mixture of Ar and C₂H₂. The effects of annealing temperature (25~100 ℃) on morphology, microstructure, mechanical properties and tribological performance were studied. The result showed that as-deposited a-Si:C films displayed a typical amorphous structure and the cross-sectional morphologies of a-Si:C films were uniform and compact, and there were no obvious cracks. No indications of discontinuities were observed between the a-Si:C film and substrate/transition layer. After annealing at lower temperature (≤ 200 ℃), the structure of a-Si:C films had no significant change, but the internal stress lineally increased, and the maximum value was 2.8 GPa at 200 ℃. Hardness (H) and elastic modulus (E) firstly increased to 18.13 GPa and 167.74 GPa at 100 ℃ from 4.14 GPa and 97.61 GPa at 25 ℃, respectively, and then decreased to 18.13 GPa and 167.74 GPa at 200 ℃. These parameters, in turn, determined the wear rate. Accordingly, the wear rate initially decreased and then increased. The films annealed at 100 ℃ exhibited the lowest wear rate due to excellent mechanical properties where the maximum values of H/E and H³/E² were obtained. The sample annealed at 200 ℃ exhibited the highest wear rate, possibly owing to its elevated internal stress. Moreover, the friction coefficient decreased due to the formation of graphitization transfer layer. At an annealing temperature of 300 ℃, the structure of films still remained the same, but the internal stress, H and E decreased slightly. Although the friction coefficient slightly increased due to surface roughening, the films showed good wear resistance, attributed to the presence of Si-C bonds that maintained structural stability. Upon annealing at higher temperatures (400 and 500 ℃), an increase in sp²-C content and surface oxidation was observed, and the higher annealing temperature, the more serious graphitization and oxidation was. Specially, a decreased thickness and loose oxidation layer were obtained at annealing temperature of 500 ℃. The internal stress, H and E decreased, and dropped sharply when annealing temperature increased to 500 ℃ from 400 ℃. But a lower friction coefficient and wear rate were achieved, resulting from the formation of a transfer film primarily composed of carbon generated from the reactions between Si-C, Si-O-C, Si-O and C-C. The relevant results provided reference for structure and property regulation and engineering application of a-Si:C films.