Si -substituted hydroxyapatite has been prepared to obtain biomaterials having an improved biocompatibility. From FT-IR, XRD, and ICP analyses, it was confirmed that the single-phase of hydroxyapatite substituted by Si has formed. Si- substituted hydroxyapatite of up to 2 wt% for Si keeps its original structures intact for the sintering temperatures of up to 1200$^{circ}C$. However, it is observed that the ion substitutions by the amount higher than the above ratios for the hydroxyapatite leads to destabilize original structures of the hydroxyapatite and to produce tricalcium phosphate and calcium phosphate silicate phases when the samples were sintered at 1l00$^{circ}C$ or higher.