Selective catalytic reduction of nitrogen oxides is an efficient technique for emission abatement in heavy-duty vehicles. Cu-SSZ-13 SCR catalysts are more active than vanadium-based catalysts at low temperatures, but are more sensitive to deactivation by sulfur. Consequently, there is a need to study poisoning by sulfur for this catalyst material. This experimental investigation focuses on the effect of sulfur on the low-temperature performance of Cu-SSZ-13 SCR catalysts. The effect of sulfur exposure temperature, and the influence of the NO2/NOx ratio, are considered and two different regeneration temperatures are compared. In addition, catalyst samples from an engine-aged catalyst are evaluated. The SO2 exposure temperature is shown to have an important impact on the deactivation of the Cu-SSZ-13 catalyst. The lowest sulfur exposure temperature (220 degrees C) results in the most severe deactivation, while the highest temperature during sulfur exposure (400 degrees C) results in the lowest degree of deactivation. This was found to be related to the amount of sulfur on the catalyst. Additionally, SO2 exposure was shown to decrease the N2O selectivity. The engine-aged catalyst has a decreased performance in terms of both decreased activity and increased N2O selectivity. For this catalyst, impurities from fuel and engine-oil can play a role in the deactivation. Different deactivation mechanisms are seen for the laband engine-aged catalysts.