The effects of different amounts of Y 2 O 3 addition (0, 0?25, 0?50, 0?75 and 1?00 wt-%) on the lattice parameters, sintering behaviour and mechanical properties of Al 2 O 3 /15 wt-%ZrO 2 porous composite ceramics have been investigated. It is found that Y 2 O 3 and Al 2 O 3 tend to form Al 5 Y 3 O 12 rather than a solid solution of (Al 1-X Y X ) 2 O 3 , while Y 3z can displace Zr 4z of ZrO 2 to form a solid solution and increase the lattice constants of tetragonal zirconia (t-ZrO 2 ). The additions of Y 2 O 3 into Al 2 O 3 /15 wt-%ZrO 2 porous composite ceramics not only stabilise t-ZrO 2 but also act as a sintering aid for promoting the sintering process. In addition, Y 2 O 3 additions are beneficial to improving the modulus of rupture and cold crushing strength of Al 2 O 3 /15 wt-%ZrO 2 porous composite ceramics; their maximum values are obtained at 0?75 wt-%Y 2 O 3 , which are 56 and 118 MPa respectively.