Platinum-loaded sulfated zirconium oxide catalyst (Pt/SO42-/ZrO2) for isomerization of light naphtha had been developed through the joint research between Cosmo Oil Co., Ltd., and Mitsubishi Heavy Industries, Ltd., in 1983. The role of small amount of noble metal in this novel catalyst is presented. Platinum improved catalyst stability by preventing formation of coke precursors on strong acid site of sulfated zirconium.After the collaboration for commercialization of this catalyst with UOP LLC for many years, we had reached to a success of the first commercial operation for naphtha isomerization catalysts in 1996. The expected performance and stability during the commercial operation of Par-Isom have been obtained. (C) 2003 Elsevier Science B.V. All rights reserved.