Hydroxyapatite (HAp: Ca-10(PO4)(6)(OH)(2)) was synthesized by aqueous precipitation using CaCl2 and Na3PO4 with NaOH added to ensure completion of the reaction at room temperature. The HAp powder prepared using stoichiometric amounts of NaOH was stable even at 1200 degrees C, but the HAp prepared with sub-stoichiometric amounts of NaOH resulted in its transformation into beta-tricalcium phosphate at 600 degrees C. The reaction pH, X-ray diffraction, thermal analysis, scanning electron microscopy, Fourier transform infrared analyses and inductively coupled plasma-optical emission spectroscopy were used to characterize the phase purity, thermal stability, morphology, and chemical composition of the synthesized HAp powder.