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 NH 3 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 electron microscopy, N 2-adsorption, temperature-programmed desorption, and X-ray photoelectron spectroscopy. The analysis indicates that Mn 2 O 3 , Mn 3 O 4 , and amorphous MnO 2 coexist on the surface of the Mn/SSZ-13 catalysts, with MnO 2 comprising the largest proportion, which may contribute to the high SCR activity. Additionally, the specific surface area and pore volume both decrease with increasing Mn loading. The Mn/SSZ-13 catalyst with 4.74 wt% of Mn has a high concentration of lattice oxygen, a high amorphous MnO 2 content, and greatest number of strong Lewis acid sites, which are beneficial to the adsorption of NH 3 , and may account for its superior catalytic activity.