Cadmium sulfide coated zinc oxide hierarchical nanocomposites have been synthesised at room temperature by a simple solution based method. CdS nanoparticles were deposited on the surface of ZnO without using any surfactant, ligand or chelating agents. The nanocomposites were synthesised using different concentrations of thioacetamide, cadmium salts, and also by varying the reaction time. After characterization of the nanocomposites, optical properties were investigated by UV-visible diffuse reflectance and photoluminescence spectroscopy techniques. It was found that band gap of the ZnO-CdS nanocomposites is tunable between 2.42 and 3.17 eV. (C) 2012 Elsevier Ltd. All rights reserved.