A method for producing poly(dimethyl vinylphosphonate) from a monomer component mainly containing dimethyl vinylphosphonate by anionic polymerization in the presence of an anionic polymerization initiator, the method being characterized in that an aliphatic ether is used as a polymerization solvent, and a method for producing poly (vinylphosphonic acid) characterized in that the poly(dimethyl vinylphosphonate) obtained by the former method is hydrolyzed in the presence of an acid are provided. The methods make it possible to easily produce a poly(dimethyl vinylphosphonate) which has a high molecular weight and in which the molecular weight is controlled, and make it possible to produce a poly (vinylphosphonic acid) which has a high molecular weight and in which the molecular weight is controlled corresponding to the poly(dimethyl vinylphosphonate).