The objective of this study is to investigate the effects of magnesium oxide doping on the microstructure and mechanical property of sintered yttria (3 mol%)-stabilized zirconia (YSZ) composites. Well-dispersed (80/20) YSZ/ Al2O3 ceramics containing 25 ppm, 100 ppm, 250 ppm, and 1 wt% MgO were prepared by solid state reaction method. The relative density, average grain size, lattice parameters, microhardness, and fracture toughness of MgO doped YSZ/Al2O3 ceramics sintered in the temperature range of 1,250~1,500℃ were investigated. Experimental results showed that the composite with 100 ppm MgO and sintered at 1,400℃ has a bulk density of 96.8%, 1,168 in Vickers hardness, 4.87 MPa‧m^1/2 in toughness, and 482 MPa in flexural strength.