Nanophase alpha-alumina and hydroxyapatite composites (with and without 5 wt% AlF3, CaF2 or MgF2 added separately) were hot pressed at 1100 degrees C and 1200 degrees C to investigate their mechanical properties and phase stability. Hydroxyapatite slightly decomposed to tri-calciurn-phosphate when there was no F- present. With the addition of AlF3, CaF2 or MgF2 into the composite, it improved its thermal stability and mechanical properties. Substitution of OH- by F- ions in hydroxyapatite was verified by the change in hydroxyapatite's hexagonal lattice parameters and unit cell volume. A fracture toughness of 2.8 MPa root m and mu-hardness of 8.25 GPa were calculated for the composite containing CaF2 after the hot pressing at 1200 degrees C. (C) 2007 Elsevier Ltd. All rights reserved.