Hydroxyapatite (HA) is extensively used in medicine as an ideal substitute for bone. Mean particle size, particle size distribution critically influence the hardness of HA and its mechanical properties. Statistical design was used to determine the optimum conditions of HA preparation by mechanochemical-hydrothermal procedure in MICROS mill for varying times, speed of milling as well as the quantity of surfactant. The produced powder was subjected to X-ray diffraction to analyse its crystallinity, phases, and crystal size calculations using Scherrer's equation. Reaction and milling time seems to be the most significant factor in determining particle size, the longer the reaction and milling time the smaller the crystal size with crystallite sizes ranged from 5.55 to 23.9 nm. (C) 2008 Elsevier B.V. All rights reserved.