To provide a new cyclic phosphoric acid ester produced by reacting 2,2-dimethyl-1,3-propanediol with phosphorus oxychloride and reacting the product with a phenolic compound in the presence of a catalyst and useful e.g. as a halogen-free flameproofing agent.

This new halogen-free cyclic phosphoric acid ester is expressed by the formula I (R is 2-methylphenyl, 3-methylphenyl, 4-methylphenyl, 2,3- dimethylphenyl, 2,4-dimethylphenyl, 2,5-dimethylphenyl or 3,4-dimethylphenyl) and is useful as a flameproofing agent, etc. The compound can be produced by reacting 2,2-dimethyl-1,3-propanediol of the formula II with phosphorus oxychloride and reacting the resultant cyclic phosphoric acid ester chloride of the formula III with a phenolic compound of the formula, ROH in an inert solvent in the presence of a t-amine.