The thermal behaviour of cellulose acetate films in which hexamethoxycyclotriphosphazatriene or polymethoxyphosphazene had been dispersed was studied by differential thermal analysis (DTA) and thermogravimetric analysis (TGA). The thermograms obtained under the atmospheric condition resembled those previously reported elsewhere for cellulose treated with flame retardants in the conventional manner. It was found that the thermal degradation of the flame retardant films began at a lower temperature than that of the control. Compared with the control, the flammable volatile matter evolved much smaller whereas much more residue remained when the pyrolysis completed. The total area of the exothermic peaks for the flame retardant film was also much smaller than that of the control. The LOI(limited oxygen index) of cellulose acetate film increased in proportion to the percentage of flame retardants.