A series of Zn1-xCuxS nanoparticles with dopant content ranging from x=0.00 to 0.15 was prepared in water using microwave irradiation. The nanoparticles were investigated by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and UV-Vis diffuse reflectance spectra (DRS) techniques. It was found that Cu2+ ions are homogeneously substituted for Zn2+ ions in ZnS lattice. The absorption edges for Zn1-xCuxS nanoparticles are red-shifted as content of Cu2+ ions increases. The SEM images demonstrate that the nanoparticles are nearly spherical and the size decreases with Cu2+ content. Photocatalytic degradation of methylene blue (MB) on the prepared nanoparticles was investigated under visible light irradiation. The results indicate that Zn0.97Cu0.03S nanoparticles exhibit highest photocatalytic activity among the prepared samples. Increasing photocatalytic activity of Zn0.97Cu0.03S nanoparticles has been attributed to its high visible light absorption and decrease of electron-hole recombination due to presence of Cu2+ ions in the lattice. Moreover, the reaction rate constant decreases with microwave irradiation time applied for preparation of the nanoparticles and calcinations temperature. (C) 2010 Elsevier B.V. All rights reserved.