8 mol.% yttria-doped cubic zirconia (8Y-CSZ)/AI203composites containing 0–30 vol.% AljOj particles were fabricated by sintering, followed by hot isostatic pressing (post-HIPing). All composites were densified to at least 99.5% of the theoretical density by post-HIPing. The bending strength of composites sintered at 1500°C in air was independent of A1203 content, but a significant improvement in the bending strength was achieved by the post-HIPing technique. The bending strength and the fracture toughness of the HIPed composites increased with increasing a1j03 content. Ionic conductivity of the composites was evaluated and the total, lattice, and grain boundary conductivities slightly decreased with increasing Al2, content. The HIPed composites containing up to 20 vol.% A1203 appear to be suitable candidate materials as electrolyte for solid oxygen fuel cell.