In this study, undoped and Er-doped PbSe (ErxPb1-xSe) nanoparticles were successfully synthesized through a facile hydrothermal method. Synthesized nanoparticles were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and photoelectron spectroscopy (XPS) techniques. Photocatalytic activity of undoped and Er-doped PbSe was evaluated by photocatalytic decolorization of Malachite Green (MG) under visible light irradiation. XRD analysis confirmed that the samples were crystallized in face-centered cubic PbSe phase. SEM images demonstrated that the size distributions of the undoped and 4% Er-doped PbSe particles were in the range of 60-70 nm and 50-60 nm, respectively. XPS analysis represented that Er ions were successfully incorporated into the PbSe crystal lattice. Decolorization efficiency was increased from 64.89%, in the presence of undoped PbSe, to 95.60% in the presence of 4% Er-doped PbSe at 75 min of irradiation time. The order of inhibitory effect of different inorganic ions was found to be as Cl- > F- > HCO3- > CO32-. The presence of peroxydisulfate as enhancer significantly increased the decolorization efficiency. Synthesized nanoparticles exhibited good reusability after 10 sets of photocatalytic reaction. The photocatalytic degradation process can be explained in terms of pseudo-first-order kinetic model. The main degradation intermediates produced in the photocatalytic degradation of MG were identified by gas chromatography coupled to mass spectrometry (GC-MS) analysis, and a possible pathway was proposed. (C) 2014 Elsevier B.V. All rights reserved.