On-board liquid hydrocarbon reforming with the aid of supported transition metal catalysts is attracting considerable attention as it is very promising for providing H2 to fuel cell-powered vehicles. However, the catalyst deactivation due to carbon deposition and sulfur poisoning is a big challenge for its practical applications. In this study the deactivation of Al2O3 supported Rh, Pt, Ru, Pd, and Ni catalysts is investigated through liquid hydrocarbon reforming in the absence and presence sulfur. For the reactions without sulfur, the Rh, Pt, and Ru catalysts exhibited comparable catalytic performance, which were better than the Pd and Ni catalysts. With the presence of sulfur, all the catalysts were severely poisoned by sulfur with remarkably increased carbon deposition except the Rh catalyst. The superior sulfur tolerance of Rh can be mainly attributed to its strong capability in the conversion of sulfur to sulfonate and sulfate. Moreover, K is effective in enhancing the catalytic performance of the Ni catalyst in the reactions with sulfur due to its beneficial effect on the reduction of carbon deposition, whereas only little promotion effect of K is observed for the noble metal catalysts.