The microstructure of Al2O3 reinforced hydroxyapatite (HA-Ca5(PO4)3OH) was studied. It was demonstrated that in this composite the Al2O3 particles are uniformly distributed in a matrix of spherical HA agglomerates formed by primary needlelike HA particles present before making green compact. In the HA + 20 wt% Al2O3 system, hydroxyapatite is partially decomposed into alpha-Ca3(PO4)2 and CaO with H2O vapour during sintering. Subsequently, the CaO is combined with Al2O3 to produce calcium aluminates (CaAl2O4 and CaAl4O7).