Composites of mullite and zirconia were fabricated via the cyclic infiltration of porous zirconia-based preforms with a liquid mullite precursor. The maximal amount of mullite precursor that could be infiltrated was dependent primarily on the initial open porosity of the preforms, When a zirconia preform with an initial open porosity of similar to 58% was cyclically infiltrated to saturation, the open porosity was reduced to similar to 43%, with a median pore diameter of 15 nm, After sintering at a temperature of 1500 degreesC for 2 h, the saturation-infiltrated zirconia preforms could be densified to similar to 98% of the theoretical density. In zirconia samples, infiltrated mullite had a tendency to coalesce into large, elongated grains as the sintering temperature was increased. The presence of infiltrated mullite did not have a significant effect on the zirconia grain structure. The distribution of mullite in the samples was nonuniform, and the distribution profiles varied as the number of infiltration cycles varied. Although the sintered density and hardness showed small improvements after saturation infiltration, the fracture toughness did not increase.