Nanoparticles of Zn1-xCuxS with various dopant contents (0 <= x <= 0.15) were prepared in water by refluxing for 90 min at about 95 degrees C. Powder X-ray diffraction (XRD) patterns of the nanoparticles demonstrate that loading of Cu2+ ions does not change the crystal structure of ZnS. Scanning electron microscopy (SEM) images demonstrate that size of the nanoparticles decreases with increasing Cu2+ ions. UV-Vis diffuse reflectance spectra (DRS) of the nanoparticles show significant absorption in visible light region. Adsorption capacity of the nanoparticles for methylene blue (MB) increases with mole fraction of copper ions. Photocatalytic activity of the nanoparticles toward photodegradation of MB was evaluated under visible light irradiation. The results indicate that Zn0.85Cu0.15S nanoparticles exhibit highest photocatalytic activity among the prepared samples. Moreover, effects of refluxing time applied for preparation of the nanoparticles and calcination temperature were investigated. (C) 2010 Elsevier B.V. All rights reserved.