Yttria-stabilized zirconia (YSZ)/hydroxyapatite (HAp) composite nanopowder was synthesized using a chemical precipitation and calcination process. Each YSZ/HAp gel powder showed an averaged particle size of similar to50-100nm and it was dried and calcined for crystallization. The crystallization characteristics of each powder were analyzed using X-ray diffraction (XRD) and quantitative analyses were performed on each phase using quantitative XRD (Q-XRD). The formation of beta-tricalcium phosphate (beta-TCP) was controlled changing the Ca/P ratio in HAp phase and also YSZ content in the composite nanopowder. It was revealed that beta-TCP content showed a minimum value at Ca/P ratio of similar to1.73 and at YSZ content of 10wt%, respectively. The mechanism of increased beta-TCP content with Ca/P ratio lower than 1.73 and increased beta-TCP content with YSZ content was explained as Ca-deficiency due to the Ca-diffusion into t-ZrO2 crystals to form a solid solution, which was confirmed analyzing the lattice parameter change of t-ZrO2 crystals. The composite nanopowder with Ca/P ratio of 1.77 showed formation of CaO crystals, resulting in the increase in beta-TCP content., (C) 2003 Elsevier Science B.V. All rights reserved.