Sulfur addition is used to probe the role of gold in Au/Fe₂O₃/ZrO₂ catalyst in the water-gas shift (WGS) at high temperature (623-773 K) and pressure (21 bar). Sulfur poisoning unravels the WGS activity contribution by gold nano-particles and gold promotion of iron oxide in Au/Fe₂O₃/ZrO₂. The active site(s) on gold nano-particles are poisoned by sulfur, which is reflected in a suppressed WGS activity of presulfided Au/ZrO₂. The same holds for the WGS activity contribution of gold nano-particles in Au/Fe₂O₃/ZrO₂, but the promotion by gold of the Fe₂O₃ is still present after presulfidation. The WGS performance of Fe₂O₃/ZrO₂ and Au/ZrO₂ catalysts with and without sulfur pretreatment are also compared with that of Au/Fe₂O₃/ZrO₂.