The phase stability, mechanical and in vitro bioactivity properties of hydroxyapatite/alumina composite with and without yttria were investigated. Hydroxyapatite without additives decomposed at 1300 degrees C to beta- and alpha-tricalcium phosphate and calcium oxide phases. Although alumina contributed to the mechanical properties of hydroxyapatite, it not only decreased the decomposition temperature of hydroxyapatite from 1200 degrees C to 900 degrees C and it's in vitro bioactivity property but also increased the decomposition ratio of hydroxyapatite. An improvement in the properties of hydroxyapatite/alumina composite was provided by yttria via inhibiting the solid-state reactions between hydroxyapatite and alumina via the formation of yttrium aluminum oxide and calcium yttrium trialuminum oxide phases. The maximum fracture toughness of 2.178 +/- 0.251 MPam(1/2), microhardness of 4.947 +/- 0.191 GPa, a compressive strength of 227.75 +/- 27.87 MPa, and a three-point bending strength of 90.15 +/- 6.93 MPa were achieved for hydroxyapatite/alumina composite containing 1.5 wt% yttria at the sintering temperature of 1200 degrees C. The relative density of 92.94 +/- 0.11% was also attained. This ternary composite can potentially be used in the human body for load-bearing applications because of its sufficient mechanical and in vitro bioactivity properties with a decomposition ratio of 9.4%.