The isomerization of the pentane that contains sulfur of 135 ppm as an ethylmethyl sulfide was studied over Metal/SO42-/ZrO2 catalysts. Pd/SO42-/ZrO2 catalyst possessed stable isomerization activity and hydrodesulfurization (HDS) activity simultaneously, although the isomerization activity Of Pt/SO42-/ZrO2 catalyst is weakened by the sulfur that is contained in the feed. Pd has the functions not only of the formation of carbenium ion from pentane but also of the desulfurization into H2S from organic sulfur compounds. Pd seems to remain always in an activated state so that adsorbed sulfur can desorb promptly from the catalyst. The IR spectra of pyridine adsorbed on Metal/SO42-/ZrO2 catalysts were measured in order to analyze the reaction mechanism of sulfur-containing pentane. The IR spectra of pyridine adsorbed on spent Metal/SO42-/ZrO2 catalyst are obtained only on Lewis acid sites, although fresh catalysts are observed on both Bronsted acid sites and Lewis acid sites. This result shows that the isomerization reaction of pentane advances with the Lewis acid sites and the metal that causes the formation of carbenium ion. However, the Lewis acid sites are not observed with the Pt/SO42-/ZrO2 catalyst deactivated by sulfur. The sulfur adsorption on Pt causes the disappearance of the formation ability of atomic hydrogen, and carbon accumulates on the Lewis acid sites. On the other hand, the Pd/SO42-/ZrO2 catalyst keeps the Lewis acid sites even after the isomerization reaction of sulfur-containing pentane. The Lewis acid sites are not covered with carbon so that Pd has the functions of the desulfurization of sulfur compound and the supply of atomic hydrogen to SO42-/ZrO2. Therefore, the Lewis acid sites are the main active sites in the skeletal isomerization reaction of sulfur-containing pentane over Pd/SO42-/ZrO2 catalyst, and the sulfur tolerance of this catalyst can be explained by the hydrodesulfurization function of Pd and by the hydrogen supply to the Lewis acid sites. Published by Elsevier B.V.