A new Cu/K2Ti2O5 catalyst has been developed recently to remove NOx through the NOx storage-reduction (NSR) process. However, its NSR performance in the presence of sulfur has not been investigated. In this article, the sulfur poisoning of the NOx storage reduction catalyst Cu/K2Ti2O5 and the corresponding deactivation mechanisms are reported for the first time. The effect of the sulfur concentration, adsorption/regeneration cycling tests, and temperature-programmed regeneration are studied. At low temperatures, the poisoning effect is negligible when the SO2 concentration is lower than 20 ppm, and the sulfated samples can be easily regenerated by 3.5% H-2 at 550 degrees C. However, at high temperatures, the sulfur species are adsorbed on K+ sites to form K2SO4 and, consequently, induce a structure transformation from K2Ti2O5 to K2Ti6O13 nanoparticles. The structural change is reversible, and the sulfated catalyst can be regenerated by hydrogen at 650-700 degrees C.