In this study, the synthesis of silver-zinc oxide (Ag-ZnO) nanostructures with a plant-extract-mediated hydrothermal method was investigated. The eco-friendly plant extract Azadirachta indica (Neem) was used as a reducing agent. The X-ray diffraction patterns showed the formation of face-centered cubic (fcc) Ag nanoparticles (NPs) and a wurtzite ZnO structure. An optical study of these nanostructures revealed two absorption edges: one at 393 nm corresponding to ZnO and the other at approximately 440 nm corresponding to Ag. A morphology study showed that hierarchical ZnO nanostructures were decorated with 10-50-nm-diameter Ag NPs. The formation and growth mechanism were also examined. A photoelectrochemical study was performed to investigate the electronic interactions between the ZnO and Ag NPs in the photoanode upon exposure to light. The Ag NPs act as electron acceptors, inhibiting electron-hole recombination. The photocatalytic activity of the Ag-ZnO nanostructures was examined by observing the degradation of aqueous methylene blue (MB) dye under natural sunlight. The apparent rate constant determined for the photocatalytic degradation of MB by the Ag-ZnO nanostructures was 5.9668 x 10(-2) min(-1), which was faster than that of the untreated ZnO nanostructures (2.527 x 10(-2) mm(-1)). This plant-extract-mediated synthetic route could also be applied to the synthesis of other Ag-semiconductor oxide nanostructures. (C) 2015 Elsevier B.V. All rights reserved.