Four kinds of nickel hydroxide were prepared from different starting materials, and their properties were studied by means of X-ray diffraction, thermal analysis, and IR spectra. The nickel oxide catalysts were prepared by decomposing these nickel hydroxides in vacuo and their catalytic activity was tested for the hydrogenation of soybean oil. Consequently, it was found that nickel hydroxide prepared by urea hydrolysis was semicrystalline of hydrated structure, while the others, three kinds of nickel hydroxide precipitated by ammonium hydroxide or sodium hydroxide were all the same hexagonal system of brucite type. The various adsorbed species including nitrate ion, sulfate ion, carbon dioxide, ammonia, and urea were observed in IR spectra. Among these species, nitrate and sulfate species were so stable that they remained considerably even after evacuation at 430 ℃. These adsorbed species affected the catalytic activity profoundly. Also, it was found that NiO （N-U） catalyst exhibited higher catalytic activity than any other catalysts and showed a maximum activity after evacuation at 400 ℃ for 1.5 hrs.