The impact of hydrothermal aging on SO2 poisoning over Cu-SSZ-13 selective catalytic reduction (SCR) catalysts were investigated in this study. The catalyst samples were hydrothermally aged at various temperatures for SO2 poisoning and characterized by SO2 temperature-programmed desorption (SO2-TPD), X-ray diffraction (XRD), H-2 temperature-programmed reduction (H-2-TPR), and NH3-TPD. The performance evaluations were also performed to illustrate the impact on SCR activity and oxidation. The results showed that the Cu-SO4-like species decreased in the 750 degrees C aged sample via copper migration, while they increased in the 850 degrees C aged sample due to CuOx/CuAlOx formation. The low-temperature SCR activity and oxidation decreased due to sulfur poisoning. For the sulfated sample, however, it was determined that NOx conversion was slightly higher on the mildly hydrothermally aged sample. Furthermore, desulfation is easier for the mildly hydrothermally aged sample but more difficult for the severely hydrothermally aged sample.