Abstract: A commercial de-NO_x catalyst for selective catalytic reaction (SCR) poisoned by K₂O was regenerated with (NH₄)₂SO₄ solution. The poisoning was simulated by loading different concentrations of K₂O in the de-NO_x catalysts through wet impregnation with KNO₃ solution as the K₂O precursor. After regeneration with (NH₄)₂SO₄ solution, the poisoned catalysts exhibit effective activity under the simulated conditions of different space velocities and oxygen concentrations. The catalysts before and after regeneration were characterized by ion chromatogram (IC), nitrogen physical sorption, scanning electron microscope and energy dispersive atomic X-ray spectroscopy (SEM-Maps/EDX), and infrared spectroscopy (FT-IR). The results indicated that the regeneration process is effective to remove K₂O from the poisoned catalysts and to restore the active sites of V=O, while the surface substances and mechanical properties of the regenerated catalysts are not significantly influenced by the regeneration.