Coaxial Zn/ZnO core-shell nanocable heterostructures with diameters similar to100 nm were synthesized via thermal reduction of ZnO by H-2. The products were characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy and cathodoluminescence. In some of the samples, an epitaxial relationship was found between the Zn core and the ZnO outer shell aside from the large lattice mismatch (17%) between Zn and ZnO. Systematic studies were carried out using different fabrication parameters in order to find out the formation mechanism of the ZnO layer with different crystallinity and the origin of the epitaxy between Zn and ZnO.