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 nitrogen and phosphorus, 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 in 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 being required, high solubility of the catalyst in the polymerization media, 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 other living radical polymerization methods.