The microstructure of (0 0 1)-oriented epitaxial CeO2 thin layers grown on R-plane sapphire (Al2O3) by off-axis RF sputtering was investigated, The crystalline perfection of CeO2 layers was characterized by Bragg-Brentano X-ray spectra, rocking curves (omega-scan) and TEM. The surface morphology was controlled by AFM. The as-deposited layers display small size mosaicity ( similar to 20 nm), arcing 6-7 degrees, and surface roughness approximate to 4 nm. Our results show that the degree of epitaxy can be increased by post-deposition annealing (grain size similar to 50 nm, arcing 4-5 degrees and surface roughness approximate to 0.6 nm), Microwave properties of YBCO films deposited on the as-deposited and annealed CeO2 buffer layers are also mentioned,