The sintering behavior, mechanical properties and biocompatibility of magnesia (MgO)-doped HA/TCP biphasic ceramics were studied. Pure HA/TCP ceramics showed poor sinterability due to the phase transformation of beta- to alpha-TCP. MgO-doped HA/TCP ceramics showed high density without any phase transformation of beta-TCP up to 1300 degrees C, for MgO dopants incorporated into the beta-TCP preferably and increased thermal stability of beta-TCP. However, the addition of MgO higher than a critical content, suppressed grain growth of HA/TCP ceramics and lowered sinterability. The optimum amount of MgO doping was 1 wt%, which lead 99% relative density and higher mechanical properties than HA or beta-TCP ceramics. From in vitro test and in vivo test, 1 wt% MgO-doped HA/TCP ceramics showed a good biocompatibility without cytotoxicity. After implantation under the muscle of rabbits, beta-TCP phase was dissolved from the surface and a biological apatite covered the surface. These results proved that MgO addition increased drastically the sintering and mechanical properties of HA/beta-TCP ceramics without altering the biological safety and biocompatibility of the original composite.