A novel hydrothermal process has been developed various hydroxyapatite(HA) powder. The HA powder was investigated in different calcination temperatures over the range of 200 degrees C-800 degrees C. TG/DTA and XRD analysis revealed that at temperatures of 700-800 degrees C the decomposition processes and phase changes took place. It is due to the appearance of TCP phase substituting the HA phase. FESEM observation showed that the produced hydroxyapatite powder was extraordinarily fine with nanosize primary particles and almost evenly spherical in shaped. Its high purity proved that the powder fulfills medical requirement.