Spherical aggregates of hydroxyapatite (HAp) were prepared by the reaction with colloidal calcium carbonate (calcite slurry) and phosphoric acid and/or amonium phosphates (diammonium hydrogenphosphate and ammonium dihydrogenphosphate). Spherical aggregates prepared with calcite slurry and phosphoric acid were composed of low crystalline HAp. On the other hand, the crystallinity of HAp prepared by the phosphoration of calcite slurry with ammonium phosphates was relatively high. The average particle size of HAp aggregates was depended on the reaction temperature. Monodispersive spherical aggregates of HAp with submicron size (0.9μm) were prepared by the reaction with calcite slurry and ammonium phosphates at 85°C.