Composites of hydroxylapatite (HA) and monoclinic zirconia were hot-pressed at 1100 degrees C and 1200 degrees C under vacuum to study the phase transformations and the mechanical properties. X-ray diffraction results showed a higher phase transformation from monoclinic-ZrO2 to tetragonal-ZrO2 when the sintering temperature increased from 1100 degrees C to 1200 degrees C. HA decomposed faster when the amount of ZrO2 in the composites increased. Moreover, small amount of alpha-TCP and CaZrO3 was observed in the composites hot-pressed at 1200 degrees C. Hot-pressing at 1100 degrees C resulted in better mechanical properties than the hot-pressing at 1200 degrees C because of less reaction between HA and zirconia at 1100 degrees C. 40 wt% monoclinic zirconia and HA composite hot-pressed at 1100 degrees C resulted in promising mechanical properties which are 6.5 GPa of Vickers mu-hardness, 2.23 MPa root m of fracture toughness, and 66 MPa of diametral strength.