The microstructure of (001)-oriented epitaxial CeO 2 thin layers grown on R-plane sapphire (Al 2 O 3 ) by off-axis RF sputtering was investigated. The crystalline perfection of CeO 2 layers was characterized by Bragg-Brentano X-ray spectra, rocking curves (ω-scan) and TEM. The surface morphology was controlled by AFM. The as-deposited layers display small size mosaicity (~20nm), arcing 6-7 o , and surface roughness ~4nm. Our results show that the degree of epitaxy can be increased by post-deposition annealing (grain size ~50nm, arcing 4-5 o and surface roughness ~0.6nm). Microwave properties of YBCO films deposited on the as-deposited and annealed CeO 2 buffer layers are also mentioned.