PURPOSE: To obtain the subject polyester, capable of holding various physical properties essential to a polymer and imparting the flame resistance to the polymer and useful as fiber, films, etc., by adding a specific phosphorus compound to a dicarboxylic acid, a diol and a hydroxycarboxylic acid and carrying out the polycondensation.

CONSTITUTION: This method for producing the objective polyester is to add (B) a phosphorus compound prepared by previously reacting a compound expressed by the formula (R1 is monovalent 1-18C organic group; R2 is monovalent ester-forming functional group; A is bivalent 1-18C organic group) with a basic organic compound to (A) a dicarboxylic acid (an ester-forming derivative thereof), a diol (an ester-forming derivative thereof) and a hydroxycarboxylic acid (an ester-forming derivative thereof) so as to provide 500-40000ppm content of phosphorus in the polyester, then carry out the polycondensation and obtain the polyester.