In this paper, novel promising photoelectrochemical electrodes of CoO nanowires and cocatalyst (Ag) modified CoO nanowires are prepared and studied in photoelectrochemical water splitting exhibiting an efficient photoelectrochemical activity for the first time. Detailed growth mechanisms for CoO nanowires and CoO/Ag nanowires are discussed. The effect of Ag is investigated. The enhanced absorption spectrum and photoelectrochemical performance are characterized. The photocurrent density of CoO/Ag nanowires reaches -1.10 mA cm(-2) due to a high efficiency of light-harvesting, the high holes mobility via the direct pathways and increased interfacial electrons transfer of Ag nanoparticles. Such CoO-based catalysts may lead to effective photoelectrochemical activity and can be promising building blocks in photoelectrochemical water splitting systems.