A simple method to prepare nanocrystalline hydroxyapatite (nHAP) is performed using a precipitation method assisted with microwave heating method. This method can be reported notably with high reproducibility and productivity. The received ceramic powder possesses characteristic of needle-shaped nanocrystals with dimension about 50 nm in diameter and 200 nm in length. The particle size distribution has been confirmed being in the range of 28-159 nm. Thermal analyses revealed that nHAP has at least three thermal events influenced by elevated temperatures. Phase stability and microstructure evolution of the nHAP calcined at temperatures range between 700 and 1200 degrees C are discussed in terms of the formation of secondary phases, the decomposition of HAP releasing carbonate and water. Various experimental techniques have been employed in this work, including powder X-ray diffraction, IR spectroscopy, DSC and TGA thermal analyses, dynamic light scattering and scanning electron microscopy. (C) 2006 Elsevier B.V, All rights reserved.