The effect of sulphur and phosphorus on a Pt/SiO2–ZrO2 catalyst was studied. The laboratory accelerated sulphur (SW) or phosphorus (PW), and their co-exposure (PSW) treatments were done in gas phase for 5 h at 400 °C. The fresh and treated catalysts were characterized by XPS, FESEM-EDS, TEM-EDS, BET and BJH. The catalyst activity was tested in lean diesel exhaust gas conditions by using a gas FTIR. The value of the light-off temperature of CO and C3H6 over the studied catalysts was as follows: fresh ~ SW < PSW < PW. These results can be explained by XPS and EDS results that revealed that the amount of adsorbed sulphur was much lower than the amount of phosphorus. Based on the BET and BJH results, bigger changes in the catalyst structure were observed after the PSW and PW treatments. Therefore, the impact of sulphur was negligible in comparison with phosphorus, and the sulphur actually inhibited the deactivation effect of phosphorus.