The electronic structure and magnetic properties of a Cu adsorbed polar-ZnO surface system were investigated using the ab initio projector-augmented-wave method. It is found that the H-3 site is the most stable adsorption site of Cu adsorbed polar-ZnO surfaces with stable ferromagnetism. The Zn-terminated ZnO:Cu surface system (H-3 site adsorption) is predicted to have a half-metallic property and stable ferromagnetism of 0.72 mu(B) magnetic moments. (C) 2007 American Vacuum Society.