Hierarchical nanostructures involving primary wide-band-gap nanowires and secondary narrow-band-gap branches are promising for photovoltaic application due to their excellent properties for light harvesting and fast carrier transport. In the present work, we developed a low-temperature process for facile synthesis of ZnO/CdS hierarchical nanowires, where the primary ZnO nanowires were first prepared via a hydrothermal route and then the secondary single-crystal CdS tips were grown on the ZnO nanowires by electrochemical deposition. The as-grown hierarchical ZnO/CdS nanowires are superior in charge separation as well as carrier transport, thus achieving higher open circuit voltage, short circuit current and final conversion efficiency than the common coaxial nanocables with CdS nanocrystal shell on core ZnO nanowires.