The Co-B amorphous alloy catalyst, in the form of ultrafine particles, was prepared by chemical reduction of CoCl2 with borohydride in aqueous solution. The as-prepared Co-B amorphous catalyst exhibited excellent activity and selectivity to cinnamyl alcohol (CMO) during liquid phase hydrogenation of cinnamaldehyde (CMA). Dependence of the contents of CMA and various products on the reaction time was detected, which showed that the optimum yield of CMO (87.6%) could be obtained on the Co-B amorphous catalyst after reaction for 2h, much better than that obtained on the corresponding crystallized Co-B catalyst, or Raney Ni, or Raney Co. Kinetic studies revealed that the CMA hydrogenation reaction was zero-order with respect to CMA and first-order with respect to hydrogen. The apparent activation energy was determined as 18.0 kJ/mol. According to various characterizations, such as inductively coupled plasma (ICP), X-ray powder diffraction (XRD), X-ray absorption fine structure (EXAFS), scanning electron micrograph (SEM), X-ray photoelectron spectroscopy (XPS), temperature-programmed desorption (TPD), and hydrogen chemisorption, we investigated both the structural and surface electronic characteristics of the as-prepared Co-B catalyst, including the unique amorphous structure, the homogeneous distribution of C-B alloy particles, and the electron-interaction between Co and alloying B. The promoting effects of these factors on the catalytic behaviors of the Co-B amorphous alloy are discussed briefly.