A process of reducing unsaturated organic compounds efficiently by using industrially inexpensive and easily handleable trichlorosilane as the reducing agent to thereby obtain the corresponding reductants; and reducing agents. Specifically, a process for the preparation of reductants of unsaturated organic compounds, characterized by conducting the reduction of an unsaturated organic compound by mixing the compound with trichlorosilane in the presence of a compound capable of reacting with trichlorosilane to give a five-coordinate silicon complex, e.g., N-formylated secondary amine having 3 or more carbon atoms; and reducing agents consisting of specific silicon complexes.