Although silicon doping of amorphous carbon films can lower the intrinsic compressive stress, doping alone cannot ensure a stress free state. An additional thermal processing is needed for complete stress relaxation. This additional process can, however, alter the surface properties of the film and its relative haemocompatibility. In this study, unhydrogenated amorphous carbon film incorporated with silicon was synthesized by magnetron sputtering and annealed to relieve stress. The evolution of the bonding structure and compatibility with blood were investigated. The results showed that the clustering of the sp(2)-bonded carbon was retarded, and the amorphous network disordering was increased when annealing temperature increased to 600 degrees C. Surface thrombogenesis of the films were evaluated using in-vitro platelet adhesion assay. The static evaluation of the films incubated in human platelet-rich-plasma showed an increase in the number of adherent platelets, but with lower activation percentage. (c) 2005 Elsevier B.V. All rights reserved.