Chemical etching mechanism of ZnO (0 0 0 (1) over bar) polar surface was investigated to control surface morphology. ZnO single crystal surfaces were etched with a HCl solution, and the morphology changes were observed with an atomic force microscope; hexagonal rings formed on the (0 0 0 (1) over bar) surface due to relatively rapid etching of its terrace faces in comparison with kinks or steps of etch pits. Square patterns of Pt thin films were periodically sputtered on ZnO surfaces using a mask; after etched in HCl solution for I day, many hillocks formed with keeping the original square shape. The pattern changed into pointed pyramidal shape after long-duration etching, suggesting that the shapes were influenced by the etching along not only the vertical direction, but also a little of the parallel direction to the surface.