Nanoparticles of zinc oxide-doped ceria (3-7 nm diameter) were synthesized by soft solution chemical processes at 40degreesC and pH 6. Some zinc ions remained in the solution but cerium ions precipitated completely at pH 6. The solubility limit of ZnO in Ce1-xZnxO2-x was determined to be x = 0.561. The oxidation catalytic activity of ceria effectively decreased by doping with zinc oxide. The photocatalytic activity of undoped ceria and zinc oxide-doped ceria for oxidation of phenol was much smaller than that of titania. Zinc oxide-doped ceria showed excellent UV absorption and transparency in the visible ray region in a similar manner as that of undoped ceria. (C) 2002 Elsevier Science B.V. All rights reserved.