A series of Mn/SSZ-13 catalysts of varying Mn content were synthesized by hydrothermal and co-precipitation methods. Their performances for the selective catalytic reduction (SCR) of NO_x with NH₃ were evaluated. The results indicate that over 95% NO_x conversion was achieved at a low temperature of 150◦C with an Mn loading of 4.74 wt%. Meanwhile, the NO_x conversion rate remained greater than 90% at 450◦C. The Mn/SSZ-13 catalysts were characterized by X-ray diffraction, ultraviolet–visible diffuse reflectance spectroscopy, Raman spectroscopy, transmission electronmicroscopy,N₂-adsorption, temperature-programmed desorption, and X-ray photoelectron spectroscopy. The analysis indicates that Mn₂O₃, Mn₃O₄, and amorphous MnO₂ coexist on the surface of the Mn/SSZ-13 catalysts, with MnO₂ comprising the largest proportion, which may contribute to the high SCR activity. Additionally, the specific surface area and pore volume both decreasewith increasing Mn loading. The Mn/SSZ-13 catalyst with 4.74 wt% of Mn has a high concentration of lattice oxygen, a high amorphous MnO₂ content, and greatest number of strong Lewis acid sites, which are beneficial to the adsorption of NH₃, and may account for its superior catalytic activity.