We have successfully synthesized Sb2O3 nanostructures using ultrasonic waves. We have also synthesized a brominated compound via a simple chemical reaction. In order to improve the thermal stability of the polymeric nanocomposites, Sb2O3 and brominated compound were added to the poly methyl methacrylate (PMMA) acrylonitrile-butadiene-styrene (ABS), cellulose acetate (CA) and poly styrene (PS). The influence of flame retardant additives on the thermal properties of polymer matrixes was studied using thermogravimetric analysis (TGA) and derivative thermogravimetric analysis (DTG). We found that the thermal decomposition of the nanocomposites shifts towards higher temperatures as a result of synergistic effect between Sb2O3 and brominated compound. The nanocomposites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared (FT-IR) spectroscopy.