Homogenous precipitation and subsequent calcination has been used to synthesize ultrafine ceria from cerium nitrate and urea solution. The ceria calcined from the precursor inherit the size and morphology of it. The size and morphology of the precursor are closely related to the preparation process. The morphology, size and distribution of the precursor could be tailored by changing the reaction condition and the ageing time. Monodispersed 200 nm sized spherical particles is prepared by this method. The powder is used in the chemical-mechanical polishing of Si wafer. The average surface roughness of the polished Si wafer is 0.171 nm measured by AFM.