Noble metal nanoparticle (NP) decorated ZnO nanowires (NWs) possess unique properties for photocatalytic transformations. The noble metal-ZnO nanostructures can be considered as a type of Schottky photochemical diode. When noble metal NPs are loaded onto ZnO NWs to form metal/ZnO nanocomposites the photocatalytic efficiency and photoelectric energy conversion can be significantly enhanced. The photocatalytic properties of noble metal-ZnO nanocomposites depend on the quality of their interfacial structures. Epitaxial growth of noble metal NPs onto ZnO NWs not only provides high-quality interfaces but may also stabilize the metal NPs during a liquid phase photocatalytic reaction. We studied the nucleation and growth processes of noble metal NPs onto ZnO NWs and investigated the stability of the metal NPs under aqueous environment and light illumination. We have explored a range of metal/ZnO NW systems including endotaxially grown Au NPs, PtZn and PdZn alloy NPs, Ag NPs and Ir single-atom chains. The photon-induced sintering behavior of these ZnO NW supported metal NPs in aqueous solutions will be discussed.