The difference of surface treatment method for ZnO single crystals and the epitaxial growth process occurred by the difference in the surface polarity has been studied. In the case of O-polar ZnO single crystal surface, annealing in ceramics box made of ZnO is effective to obtain atomically flat step and terrace surface structure. In the case of Zn-polar ZnO, chemical etching treatment is required to obtain pit free surface. The ZnO single crystal and homo-epitaxial films with atomically flat step and terrace surface structure were obtained for each polar surface. The effect of polarity on the surface treatment process and epitaxial growth process are discussed.