CuKSmx catalysts, prepared by the incipient wetness impregnation method, were investigated for the catalytic oxidation of HCl to Cl-2 and characterized by XRD, nitrogen sorption, H-2-TPR, O-2-TPD, XPS and FE-SEM to elucidate the role of SmCl3 promoter. Addition of SmCl3 improves the catalytic performance of CuKSmx catalyst for HCl oxidation, in which CuKSm25 catalyst exhibits the best catalytic activity of STY of 4.6 g(Cl2) g(cat)(-1) h(-1) and good stability under the reaction conditions of 0.1 MPa, 380 degrees C, GHSV of 6000 L kgcat(-1) h(-1) and HCl/O-2 = 2:1. Addition of SmCl3 promotes the dispersion of copper species and provides more active sites of copper species without changing the nature of active sites, which increases the catalytic activity of CuKSmx catalyst. The electron-donating effect of samarium and more surface adsorbed oxygen species of CuKSmx catalyst due to addition of SmCl3, accelerate transformation of the redox couple of Cu2+/Cu+, which is a key step in favor of the catalytic oxidation of HCl to Cl-2. Addition of SmCl3 inhibits the reaction between CuCl2 and KCl to produce the composite chloride of KCl center dot CuCl2 leading to the catalyst deactivation and can effectively prevent aggregation and loss of copper species of CuKSmx catalyst, which improves the catalyst stability.