Abstract: The effect of SO₂ on the low-temperature SCR activity and the thermal reduction regeneration for holmium-modified Fe-Mn/TiO₂ catalyst were investigated by activity assessment and various characterization methods. The deposition of ammonium sulfate ((NH₄)₂SO₄) on catalyst surface and the sulfuration of active component (MnSO₄) were proved to be the main causes for the deactivation in the presence of SO₂. The catalyst Fe_0.3Ho_0.1Mn_0.4/TiO₂ exhibited superior SO₂ durability when the concentration of SO₂ was lower than 0.04%, and the catalytic activity could markedly recover with the termination of sulfur-poisoning source. The deactivation behavior was irreversible when the concentration of SO₂ was increased to 0.1% but the poisoned catalyst could be regenerated after thermal reduction (350 ℃) for 60 min by 5% NH₃. The microstructure and physicochemical properties could be significantly restored after the thermal reduction regeneration. Moreover, the NO_x conversion could return to about 80%.