The objective of this study was to evaluate the adsorption potential of cadmium sulfide nanoparticleloaded activated carbon (CdSN-AC) for removal of reactive orange 12 (RO-12) dyestuffs from aqueous solutions. The characterization of CdSN-AC was performed by X-ray diffraction (XRD), transmission electron microscopy (TEM), and field emission scanning electron microscopy (FESEM) techniques. The effects of experimental parameters such as initial solution pH, contact time, initial RO-12 concentration, amount of CdSN-AC, and temperature on the adsorption process were evaluated in detail. The kinetic studies indicated that the adsorption process was best described by the pseudo-second-order kinetics model. The experimental data were analyzed by the Langmuir, Freundlich, and Tempkin isotherm models, and the monolayer adsorption capacity of CdSN-AC was found to be 150.0mgg1 by using the Langmuir isotherm model. The thermodynamic parameters indicated that the adsorption of RO-12 onto CdSN-AC was feasible, spontaneous, and endothermic in nature.