Abstract: To easily obtain a polyester having excellent mechanical properties, a satisfactory hue, and a high degree of flame retardancy. [MEANS FOR SOLVING PROBLEMS] The flame-retardant polyester is a polyester comprising ethylene terephthalate units as the main structural units and a phosphorus compound copolymerized or incorporated therein or is a resin composition comprising polyesters including that polyester. The flame-retardant polyester is characterized in that a polycarboxylic acid and/or polyol having three or more functional groups capable of forming an ester bond is contained in the polyester in a total amount of 0.05-2.

Abstract: The invention provides a polyester produced in the presence of a polycondensation catalyst comprising at least one compound selected from a group consisting of aluminum compounds and at least one compound selected from a group consisting of phosphorus compounds and being excellent in color tone, thermal stability, and transparency and improved in terms of insoluble particles. Particularly, the invention provides a polyester in which the content of an aluminum containing insoluble particles in the polyester is 3500 ppm or lower and a polyester which has a haze value of 2% or lower when being formed into a monoaxially oriented film. The aluminum catalyst for attaining these characteristics and properties may be polyester polymerization catalyst obtained by mixing an aluminum compound and a phosphorus compound in a solvent and has specified spectral characteristics in the side measurement of 31P-NMR spectrum and 27Al-NMR spectrum.