The development of new routes for the utilization of red mud (RM) waste is very urgent due to its huge accumulation and potential environmental harm. By taking advantage of its Fe-Al-Si-Ti composition and excellent plasticity, we developed a ball milling and acid-base neutralization method to reuse the RM waste as Fe-based denitration catalysts. The resulting RM catalysts demonstrate excellent catalytic activity and stability with >90% NO conversion above 400 degrees C in the presence of SO2 and H2O, which is even much better than that of a commercial V-W-Ti catalyst. Characterization data reveal that our treatment eliminates poisonous alkaline metal elements and increases dispersion of RM particles, making the RM active for denitration reactions. The formation of ferric sulfate species with more reducible Fe3+/Fe2+ active sites by a SO2 activation method can further enhance the denitration activity. Moreover, NH3-TPD and in situ IR results demonstrate that the NH3-SCR reaction over the RM catalyst follows the Eley-Rideal mechanism at high temperature and the increased absorption of NH3 for alkaline metal-eliminated or SO2-activated samples accounts for its high DeNO(x) efficiency. The demonstrated feasibility for reusage of the RM as DeNOx catalyst has promising industrial prospects for its extremely low cost, no toxicity, and high efficiency.