We present a new method to synthesize ZnO nanorods on zinc spheres to form a core-shell structure. Selective self-assembly growth of a shell with ZnO nanorods on a metallic Zn microsphere core has been accomplished via hydrothermal synthesis. The crystal structure, morphologies and chemical composition were characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy and energy dispersive X-ray spectroscopy. The interfacial chemistry involved in the growth of ZnO nanorods on the Zn core and a possible growth mechanism are discussed. The specific structure of the highly oriented one-dimensional nanorods may find applications in nanoelectronics, nanophotonics and nanomedicine.