Spherical zirconia particles were formed by coagulation of colloidal particles in zirconium aqueous sols followed by calcination. The zirconium sols were derived from zirconium oxychloride aqueous solutions by adjusting their pH values. The coagulation that resulted from reduction of dielectric permittivity of the sol medium was caused by the addition of propanol in the sols. The size of the spherical zirconia particles varied with the concentration of zirconium in the sols. (C) 2003 Elsevier B.V. All rights reserved.