Epitaxial ZnO films were grown on two polar surfaces (O-surface and Zn-surface) of (0001) ZnO single-crystal substrates using off-axis magnetron sputtering deposition. It was found that the two polar ZnO surfaces have different surface structure and morphology, which strongly influence epitaxial film growth. An interesting result shows that high-temperature annealing of ZnO single crystals will improve the surface structure on the O-terminated surface rather than the opposite surface. The morphology and structure of homoepitaxial films grown on the ZnO substrates were different from heteroepitaxial films grown on the Al2O3. The measurements of low-angle incident X-ray diffraction and atomic force microscopy of ZnO films indicate that the O-terminated surface is better for ZnO epitaxial film growth.