Nano-sized hydroxyapatite (HAp) powders were synthesized by a microwave-hydrothermal method using H3PO4 and Ca(OH)(2) as starting materials in a closed-vessel microwave device at 600 psi and 300 degrees C for 30 min. The applied microwave powers and mole ratio of Ca/P served as powerful factors in the synthesis of calcium phoaphate. In the case of relatively low microwave power of 450W and Ca/P ratio of 1.57, mixed calcium phosphate compounds such as Ca(OH)(2), CaHPO4 and HAp were detected in the synthesized powders. But in the case of running at 550 W, 1.67, synthesized powder showed the monophase of HAp having two kinds of morphologies. One was a needle shape with 4-15 nm in width and 20-50 nm in length, and the other was a spherical shape of 10-30 nm in diameter. The purity of nano-sized HAp powder was determined as 99.995% by ICP-MS. (c) 2005 Elsevier B.V. All rights reserved.