In this paper, the kinetics and sintering mechanism of hydro-thermally synthesized hydroxyapatite in the temperature range 900-1100 degrees C are presented. It was found that at 900 degrees C, the sintering process is very slow, whereas at 1000, 1050, and 1100 degrees C is much faster, caused by activated sintering with liquid phase/phase of solution on spots with concentrated material impurity and the formation of reaction/polyeutectic mixtures dominates. The activation energies of sintering were also determined. At all the investigated sintering temperatures, an approximate value of 90 kJ mol(-1) was found. (c) 2008 Elsevier B.V. All rights reserved.