Characterization studies of a mixed Ru-Co catalyst unsupported and supported on SiO2 were performed. We also examined the effect of the catalyst on hydrogenation of nitrile compounds. TPR shows that Co(II) in an unsupported Ru(OH)x/Co(OH)y precursor is easily reduced at around 473-573 K, whereas the hydrogen reduction of Co(II) in the Ru(OH)x-Co(OH)y/SiO2 did not occur even at 873 K. X-ray adsorption fine structure measurements indicated that both metals of the unsupported Ru/Co catalyst are reduced to their respective metallic state, and it is thought that Co-0-Ru-0 alloy is formed. However, Ru and Co exist as Ru-0 metal and Co oxide, respectively, in the case of a SiO2 supported catalyst. An unsupported Ru-Co catalyst shows higher activity for the hydrogenation of nitrile group and reductive amination of C=0 group of isophoronenitrile and the hydrogenation of nitrile groups of adiponitrile, succinonitrile, and dicyanobenzene than the SiO2 supported catalyst does. It is suggested that this high performance of the unsupported catalyst is based on the formation of Ru-0-Co-0 alloy.