Aligned CuO nanowires (NWs) were synthesized by a simple cost-effective oxidation method. They act as cores; high density CuO/ZnO core/shell heterostructure NWs were fabricated by thermal decomposition. Using the core/shell heterostructure NWs as a photoelectrode, a 0.71% photo-to-hydrogen conversion efficiency was obtained from photoelectrochemical water decomposition.