PURPOSE: Ta obtain the title new mixture containing specific two kinds of esters in high yield by using a phenolic hydroxyl group-containing phosphonitrilic acid polyhydroxyphenyl ester.

CONSTITUTION: Na salt of p-methoxyphenol wherein one OH of bihydric phenol is protected by methoxylation is reacted with phosphonitrile chloride, then with a pyridine hydrogen halide to give a phenolic hydroxyl group-containing phosphonitrilic acid polyhydroxyphenyl ester shown by formula I (A is group shown by formula II or formula III; B is A, alkoxy, aryloxy, amino, etc.; n is 3-20). Then a mixed substance of the compound shown by formula I, epichlorohydrin and water is heated to 90-105°C, reacted in the presence of an alkali to give the objective mixture containing phosphonitrilic acid polyglycidyloxyphenyl ester not substantially having residual active chlorine and a small amount of polyphosphonitrilic acid polyglycidyloxyphenyl ester.