Low hemocompatibility is a major problem of biomaterials that come in contact with blood. Surface modification has become an important way to improve the hemocompatibility of medical implants and interventional devices. Recently, researchers attempt to investigate the possibility of silicon oxynitride (Si-N-O) films to be applied as novel coating of blood-contacting biomaterials. However, no detailed investigation has been conducted. In this study, our work was focused on the optimization of the hemocompatibility of Si-N-O films prepared on single-crystal silicon wafers by unbalance magnetron sputtering (UBMS). The structure and chemical composition of films were characterized by X-ray photoelectron spectrometry (XPS), and their physical chemistry property was characterized by contact angle measurements. Platelet adhesion test was performed to investigate the platelet adhesion and activation. Our results suggested that films composed of Si3N4 and SiOx (x<2) exhibited better hemocompatibility than low temperature isotropic pyrolitic carbon (LTIC) that is a common material used in blood-contacting implants. It was also revealed that the higher N/O ratio in films composed of Si3N4 and SiOx (x<2) was attributed to the lower platelet adhesion and activation, and the interaction of samples with plasma proteins was demonstrated to play an important role in the adhesion and activation of platelets.