The mechanical properties of Al2O3-ZrO2 composites fabricated by RBAO(reaction bonded aluminium oxide) process were investigated. As the amount of ZrO2 increased the sinstered density of Al2O3-ZrO2 composites decreased slightly, but wear resistance was enhanced. Bending strength of Al2O3-ZrO2 composites increased in proportion to the amount of al in case of a fixed ZrO2 content. When the amount of Al was fixed bending strength reached its maximum value at 25 wt% ZrO2. The fracture toughness(K1c) increased with increasing content of ZrO2, but decreased with increasing Al amount. On the other hand, the fracture mode of Al2O3-ZrO2 composites was the mixed mode of inter-and transgranular fracture.