A novel phosphorus-containing copolyester (PET-co-DDP)/barium sulfate (BaSO4) nanocomposite was synthesized by in sitit polymerization. The oxygen index values of the resulting nanocomposites decreased with increasing the content of BaSO4 nanoparticles, but their anti-dripping behaviors were improved obviously through the UL-94 test. The flammability tests based on the cone calorimetry showed that the introduction of nano-BaSO4 to the copolyester decreased remarkably the heat release rate and effective heat of combustion. The thermal oxidative decomposition behaviors of PET-co-DDP/BaSO4 nanocomposites were studied by a conventional dynamic thermogravimetric analysis in a flowing air atmosphere with a heating rate of 20 degrees C/min. The activation energies determined from Kissinger method, Flynn-Wall-Ozawa method, and Friedman method had a same variation trend. (c) 2006 Wiley Periodicals, Inc.