A Ru-Zn/m-ZrO2 nanocomposite catalyst for benzene partial hydrogenation to cyclohexene was prepared by coprecipitation of ruthenium trichloride and zirconium oxychloride with ammonia, followed by hydrogen reduction in an aqueous zinc sulfate solution. By use of transmission electron microscopy (TEM), powder X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), the reduction of zinc cation to metallic zinc and the transformation of zirconium hydroxide to monoclinic zirconia were proposed and explained. The hydrogenation parameters, such as the amount of zinc sulfate in the pretreatment process, the hydrogenation temperature, the stirring rate, and the hydrogen pressure, influenced the yield of cyclohexene. The pronounced positive effect of metallic zinc in enhancing the cyclohexene yield was discussed. (C) 2004 Elsevier B.V. All rights reserved.