Zinc oxide (ZnO), cadmium-doped zinc oxide (CZO), zinc oxide/reduced graphene oxide (ZnO-rGO) and cadmium-doped zinc oxide/reduced graphene oxide (CZO-rGO) nanostructures were synthesized successfully using a simple and rapid aqueous co-precipitation method at room temperature. The structure, morphologies, composition and optical properties of these samples were characterized by x-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS), Raman and UV–vis spectroscopy, respectively. In order to achieve a synergic effect, both Cd concentration, and impact of rGO on photocatalytic performance of Cd-doped ZnO nanostructures were investigated. The photocatalytic activities of the samples were investigated with the degradation of methylene blue (MB) under sunlight and showed excellent photocatalytic degradation performance for CZO-rGO (5% Cd) compared to the other samples. Facile and low-temperature synthesis process with the excellent degradation performance demonstrates that the CZO-rGO nanocomposites have a great potential for wastewater treatment applications.