Yttria-stabilized zirconia (YSZ) ceramics doped with a small amount of hydroxyapatite (HA) were developed in order to produce a composite biomaterial with a high bioactivity as well as sufficient mechanical strength and fracture toughness for a heavy load. The maximum Vickers hardness of 964.1 Hv for HA-doped YSZ (HA-Z) composite was much greater than that of HA ceramics and almost the same as that of YSZ. The entire covering by bone-like apatite after a 5-day immersion in simulated body fluid (SBF) suggested that the HA-Z composite had bioactivities. The ion conductivity reduction of the HA-Z composite with an increasing amount of added HA was attributed to the diffusion of calcium ion from the HA to the YSZ grains caused by solid-state reactions. The HA-Z composite ceramics were recognized as osteoconductive and durable biomaterials and expected to be used in extended application fields. (C) 2004 Elsevier B.V All rights reserved.