Ceria (CeO 2 ) colloidal particles with a crystallite size of 2nm synthesized by the solvothermal reaction were coagulated with electrolyte solutions of NaNO 3 and KNO 3 as neutral coagulants and of NaOH as an alkaline coagulant. The pore structure of CeO 2 was not altered significantly by the concentration of neutral coagulants, although the surface area decreased with the increase in the coagulant concentration. On the other hand, the pore structures of the CeO 2 samples were varied by the concentration of NaOH solution; concentrated NaOH solutions elute cerium ions from CeO 2 colloidal particles, thus generating mesopores. The Ru catalyst supported on the CeO 2 samples having mesopores showed a high activity in liquid-phase oxidation of benzyl alcohol.