A fresh powder-like Pt/Al2O3 diesel oxidation catalyst was treated with sulphur (S-), sulphur-water (SW-), calcium-water (Ca-), sulphur-calcium-water (SCa-), and water (W-). BET, TEM-EDS, XPS, ICP-OES, AAS analyses and catalytic activity tests were used to find the effect of sulphur, calcium and water on the Pt/Al2O3 catalyst and its performance. Based on the ICP-OES and EDS results, sulphur was found to accumulate on the surface, whenever it was used in the pretreatments. Calcium was found in a very small amount on the Ca- and SCa-treated Pt/Al2O3 catalysts according to AAS and EDS results. For all the cases, the specific surface area was decreased after pretreatment. As expected, for the S-and SW-treated Pt/Al2O3 catalysts the light-off temperatures for CO and propene were higher compared to the corresponding fresh catalyst. Ca-, SCa-, and W-treated Pt/Al2O3 catalysts had almost the same light-off temperatures of CO and C3H6 than the fresh catalyst, instead. Based on the TEM-EDS results, the particle size of Pt and alumina washcoat microstructure was found to be unchanged after all the pretreatments. The pronounced deactivation is explained with sulphates formation on the active sites and with a decrease in the specific surface area. (C) Elsevier B.V. All rights reserved.