For the first time, nanoporous ceria and ceria-zirconia solid solutions with high surface area have been successfully synthesized directly via high-intensity ultrasound irradiation without thermal post-treatment. The ceria and the solid solutions were characterized by XRD, TEM, and nitrogen adsorption. It was found that the nanoporous structures of the materials obtained were formed by the agglomeration of monodispersed nanoparticles under high-intensity ultrasound irradiation. (C) 2003 Elsevier Science (USA). All rights reserved.