0.8 wt.% silicon-containing hydroxyapatite (Si-HA) thin films of thickness 600 nm have been successfully developed using a magnetron co-sputtering technique, through careful selection and control of the processing conditions. These films were immersed in simulated body fluid (SBF) to investigate the nucleation and growth of an apatite layer on their surfaces. A newly-formed apatite layer with similar characteristics to that of the biological bone apatite, was observed after 4 days of immersion in SBF. X-ray diffraction and infrared analyses confirmed this layer to be calciumdeficient micro-crystalline carbonate HA. These results demonstrated that the novel Si-HA films were highly bioactive and the time frame required for apatite formation was reduced by approximately 76 % (from 17 days to 4 days).