A boehmite-silica-zirconia precursor powder with a uniform spatial distribution of constitutive phases was prepared from the corresponding ternary sol by compressing the electrical double layer (EDL) without altering the magnitude of the surface potential at a pH of 3.5. Both the rheological data and the calculated potential energy of interaction indicated that the mixed ternary sol formed weakly coagulated units in a shallow potential energy well after the compression of EDL at a pH of 3.5. The effects of alpha-Al2O3 seeding on the phase-formation characteristics were then systematically examined. It was observed that the alpha-Al2O3 seeding facilitated the formation of alpha-Al2O3 but that it suppressed the growth of mullite in the alumina-mullite-zirconia composite. These observations were attributed to the epitaxial effect of alpha-Al2O3 seeds which preferentially induced the formation of corundum phase over mullite formation.