Ni/Kieselguhr catalysts have been prepared by precipitation of nickel nitrate with either ammonium hydroxide or sodium carbonate in a solution where kieselguhr particles are suspended. Changes in the catalyst proper-ties with the preparation conditions have been studied primarily by observing the X-ray diffraction patterns of the sam-ple catalysts. The amount of nickel silicate formed on the catalyst surface during the precipitation step is closely related to the pro-perties of the catalysts. That is, formation of nickel silicate on the catalyst increases the total surface area of the catalysts, and reduces the nickel particle size as well as its reducibility. Nickel silicate is enhanced on the catalyst when the alkaline precipitant, preferably sodium carbonate than ammonium hydroxide, is injected slowly into the nickel nitrate solution which is maintained at high temperature. Aging of the precipitation solution at high pH after fast precipitation enhances the formation of nickel silicate on the catalyst, particularly when sodium carbonate is used as a precipitant. However, when ammonium hydroxide is used as a precipitant, slow precipitation without aging is more effective for the nickel silicate formation than fast precipitation followed by aging. The hydrogenation rates of unsaturated fatty acid on the nickel catalysts decrease significantly when nickel silicate is formed on the catalyst to certain extents. This seems to result from retarded diffusion of the large reactant molecules into the catalyst pores, whose opening size has been reduced by the nickel silicate formation.