Nanoparticles of zinc oxide-doped ceria (3–7 nm diameter) were synthesized by soft solution chemical processes at 40 °C 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.