Epitaxial,c‐oriented YBa2Cu3Oxthin films were deposited by dc sputtering on (11¯02)‐sapphire substrates with an intermediate buffer layer of Y‐stabilized ZrO2(YSZ), which was grown by rf magnetron sputtering. The epitaxy of the YSZ and the YBa2Cu3Oxfilms was proved by Rutherford backscattering spectrometry combined with ion channeling. The YBa2Cu3Oxfilms exhibited transition temperatures of 90 K and had critical current densities exceeding 1.2×106A/cm2at 77 K in zero magnetic field.