The bimetallic amorphous alloys Ni-Co-B were prepared by the chemical reduction of the solution containing both nickel and cobalt salts with aqueous potassium borohydride. Those samples were thoroughly characterized by ICP, BET, DSC, XRD, EXAFS, XPS, TEM and TPR. Superior to the rapid quenching techniques, the content of Co in Ni-Co-B alloys could be adjusted in a wide range by changing the initial concentration of cobalt salt in the solution. The catalytic activities of the as-prepared materials were measured through the hydrogenation of benzene under moderate pressure in liquid phase. By comparing with the activities of the corresponding pure Ni-B, Co-B and their mixture as well as the Ni-Co-B amorphous alloys with different contents of Co, both the inhibiting and promoting effects of Co on the hydrogenation activities in Ni-Co-B amorphous alloys have been observed and discussed according to the amount of the effective metal in the alloys and their structural characters, especially their surface properties.