In this study, cobalt sulfide-reduced graphene oxide (CoS-rGO) nanocomposite was prepared by a solvothermal route and its structure, morphology and composition were assessed using various techniques, including transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA). The catalytic performance of CoS-rGO was evaluated for activation of peroxymonosulfate (PMS) for the elimination of rhodamine B (RhB) and pentachlorophenol (PCP) in water. The effects of various operating parameters on the degradation efficiency were systematically studied. Under optimized operating conditions, the CoS-rGO/PMS system achieved fast (less than 10 min) elimination of RhB and PCP at room temperature, as evidenced by high-performance liquid chromatographic (HPLC) analysis. Electron Paramagnetic Resonance (EPR) studies along with scavenging experiments revealed that sulfate radicals () were the primary players in the catalytic process. Interestingly, the CoS-rGO catalyst was stable after 8 cycles without obvious activity loss. The results reported in the present study hold promise for potential application of CoS-rGO for PMS activation for the elimination of various organic pollutants.