The influence mechanisms of SO2 on selective catalytic reduction (SCR) of NO over activated carbon honeycomb supported MnOx (Mn/ACH) and CeO2-MnOx (CeMn/ACH) catalysts were investigated at low temperature. The catalysts under different conditions were characterized by transient response experiment, nitrogen adsorption, X-ray diffraction, and X-ray photoelectron spectroscopy techniques. Results indicate that SO2 deactivates the SCR activities of Mn/ACH and CeMn/ACH catalysts at 160 degrees C. The deactivation is mainly due to the deposition of ammonium sulfite and ammonium sulfate on the catalysts surfaces during the NO removal process in the presence of SO2. Compared with Mn/ACH, CeMn/ACH catalyst exhibits a higher resistance to SO2 poisoning, because the addition of CeO2 inhibits the formation of ammonium salts. These ammonium salts decrease SCR activities through pore blocking; however, they can be completely removed by thermal regeneration at 350 degrees C. Furthermore, the competitive adsorption between SO2 and NH3 also decreases SCR activities.