We report on the epitaxial growth and characterization of yttria-stabilized zirconia (YSZ) films on X-cut LiNbO3 single crystals. Epitaxial (100) YSZ films were synthesized by the on-axis RF magnetron sputtering technique. Extensive analyses of the structure and microstructure of films with different thickness reveals the existence of an Li-deficient phase, LiNb3O8, at the interface between the substrate and the film. The origin of the presence of this interface is discussed. as well as its consequences on the structural and morphologic properties of the epitaxial YSZ film.