Abstract: Fe(OH)₃ and Fe₂O₃ were first prepared by a precipitation method and then sulfated to obtain the SO₄^2--functionalized SO₄^2-/Fe(OH)₃ and SO₄^2-/Fe₂O₃ catalysts for the selective catalytic reduction of NO_x with NH₃ (NH₃-SCR); the promoting effect of SO₄^2- functionalization on the performance of Fe₂O₃ catalyst in NH₃-SCR was then investigated. The results indicate that the SCR activity of the SO₄^2--functionalized Fe₂O₃ catalysts is significantly improved in comparison with that of unmodified Fe₂O₃. In particular, the SO₄^2-/Fe(OH)₃ catalyst exhibits excellent performance in NH₃-SCR, with the NO_x conversion of over 80% at 250-450 ℃; besides, it also display high catalytic stability and resistance towards H₂O + SO₂. A series of characterization results including XRD, Raman spectroscopy, TG analysis, FT-IR spectroscopy, H₂-TPR, NH₃-TPD and in situ DRIFTS reveal that the functionalization with sulfuric acid can inhibit the growth of Fe₂O₃ grains; moreover, SO₄^2- combines with Fe³⁺ to form the sulfate complex, leading to an increase in the number of surface acid sites and the acid strength, which can inhibit the ammonia over-oxidation on Fe₂O₃ and enhance the deNO_x performance of Fe₂O₃.