Provided is a low-cost, highly active, environmentally friendly living radical polymerization method which does not require a radical initiator. Even if a catalyst is not used, a living radical polymerization method can be conducted by controlling the amount of the oxygen in the gaseous phase in the reaction vessel within a suitable range. A monomer having a radical-reactive unsaturated bond can be subjected to a radical polymerization reaction to obtain a polymer having narrow molecular weight distribution. The cost of the living radical polymerization can be remarkably reduced. The present invention eliminates the disadvantages of the conventional catalysts such as toxicity, low solubility, coloring/odor and the like, and is significantly more environmentally friendly and economically efficient than conventional living radical polymerization methods.