Multiphase composites of yttria- and ceria-doped tetragonal zirconia agglomerates (10-50 mum) dispersed into an alumina or alumina-zirconia matrix were sintered at 1500-1600-degrees-C in air, followed by post-Hot Isostatic Pressing (HIP) at 1450-degrees-C and 150 MPa in an Ar gas atmosphere. The relative density of the recovered composites was above 98% of the theoretical density. By chemically etching on the surface of zirconia agglomerates, the sinterability of composites was apparently improved; and no microcracks nor pores were observed at the interface of agglomerate and matrix. According to scanning electron microscopy (SEM) observation, tetragonal and tetragonal monoclinic zirconia agglomerates were highly dispersed into the alumina or alumina zirconia matrix. The multiphase composites containing 10 vol% spherical agglomerates demonstrate the relatively low value of bending strength, < 400 MPa, and a high value of fracture toughness, > 11 MPa m1/2. The crack propagation introduced by Vickers indentation was efficiently suppressed and deflected by the agglomerates.