Epitaxial ZnO films were grown on two polar surfaces (O-surface and Zn-surface) of (0 0 0 1) ZnO single crystal substrates using off-axis magnetron sputtering deposition. As a comparison, films were also deposited on (0 0 0 1) Al2O3 substrates. It was found that the two polar ZnO surfaces have different photoluminescence (PL) spectrum, surface structure and morphology, which strongly influence the epitaxial film growth. The morphology and structure of homoepitaxial films grown on the ZnO substrates were different from heteroepitaxial films grown on the Al2O3 An interesting result shows that high temperature annealing of ZnO single crystals will improve the surface structure on the O-surface rather than the Zn-surface. The measurements of PL, 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.