ZnO/CdS core-shell hetero nanostructures with different shell thickness have been successfully developed by a solution chemistry method employing rapid homogenization concept. The obtained core/shell nanoparticles were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray analysis (EDX), FTIR, Raman, photoluminescence (PL), and UV-visible spectroscopy. All analytical and spectroscopic tools supported the formation of CdS shell over ZnO core. ZnO/CdS core-shell nanostructures were evaluated for their photocatalytic activity against methylene blue (MB), a common industrial water pollutant. It was observed that the ZnO/CdS core-shell nanostructures can effectively function as a photocatalyst under both UV and sunlight for degradation of MB. It was also observed that the degradation of MB was higher from core/shell nanostructures than the physical mixture of ZnO-CdS which was prepared separately.