A highly active and environment-friendly catalyst for use in a living radical polymerization is provided. A catalyst for use in a living radical polymerization method is provided. The catalyst comprises a central element, which is selected from germanium, tin and antimony, and at least one halogen atom, which is bound to the central element. A monomer having a radical reactive unsaturated bond is subjected to a radical polymerization reaction under the presence of the catalyst, thereby it is possible to obtain a polymer having narrow molecular weight distribution. The present invention has the merits such as low toxicity of the catalyst, a small amount of the catalyst can be used, high solubility of the catalyst, mild reaction conditions, no coloration, no odor (unnecessary post-treatment of molded products). The method of the present invention is more environment-friendly and economical than a conventional living radical polymerization method.