Perfect epitaxial growth of superconducting YBa2Cu3O7−xthin films have been achieved on (100) SrTiO3, (110) SrTiO3, and (100) ZrO2substrates using a modified planar dc magnetron sputtering system. The films exhibit zero resistances at 87–90 K with transition widths of about 2 K. The critical current density of 1.4×106A/cm2at 77 K so far has been measured on the (100) SrTiO3substrate. The epitaxial orientation of the thin films was influenced by the substrate orientation, the substrate temperature, and the oxygen partial pressure. The quality of growth and the epitaxial orientation of the films were examined by electron channeling, x‐ray diffraction, and reflection high‐energy electron diffraction techniques. The preferential epitaxial orientation is discussed.