The isomerization reaction of sulfur-containing light naphtha was studied. The Pd/SO42-/ZrO2-Al2O3 catalyst in which the active metal was modified into Pd indicates the stable isomerization activity, although the isomerization activity of the conventional pt/SO42-/ZrO2-Al2O3 catalyst decreases due to the existence of sulfur in the feed. But the increase of sulfur content in feed caused a drop of the isomerization level over Pd/SO42-/ZrO2-Al2O3 catalyst. The increase in the amount of sulfur supplied to the catalyst invites the increase of the amount of Pd required for a desulfurization reaction, and leads to the decrease in the relative amount of Pd that performs the homogeneous dissociation of gaseous hydrogen. By preparing the catalysts so that the methods of the Pd addition are different, one could study the correlation between the position of Pd in SO42-/ZrO2-Al2O3 carrier and the isomerization activity. The catalyst, which forms Pd/Al2O3 shows the highest isomerization activity. This fact suggests that the optimal position of Pd in SO42-/ZrO2-Al2O3 carrier is on Al2O3 and that the high desulfurization function is obtained by the formation of Pd/Al2O3. Furthermore, we researched about a catalyst that would work effectively in the isomerization of light naphtha, which contains sulfur in high concentrations. The catalyst where Pd is impregnated into Pt/SO42-/ZrO2-Al2O3 can obtain the stably high activity in the isomerization of light naphtha that contains sulfur of 490 massppm at a reaction temperature of 200degreesC. The results of EPMA analysis indicate that this catalyst forms a unique hybrid structure where Pt exists on zirconia and Pd exists on alumina, respectively. The high sulfur tolerance of hybrid-type catalyst is brought about by the isomerization function of pt/SO42-/ZrO2 particles and the hydrodesulfurization function of Pd/Al2O3 particles. We propose a model of the optimal metal position for the isomerization of light naphtha, which contains sulfur in high concentration, and we consider more deeply about the catalytic action of the hybrid-type catalyst. (C) 2004 Elsevier B.V. All rights reserved.