The main purpose of this study is to investigate the effects of nanoclays on the flammability behavior of neat polystyrene and polystyrene compounded with traditional flame retardants triphenyl phosphate and its synergist melamine cyanurate. Nanocomposites were prepared via ultrasound-assisted solution intercalation technique. Dispersion and nanomorphology of nanoclays were investigated through X-ray diffraction analysis and transmission electron microscopy. Thermal stability and flammability behaviors were evaluated by thermogravimetric analysis, limiting oxygen index, and mass loss calorimeter tests. These analyses indicated that addition of only 5% nanoclays resulted in significant improvements in many flame retardancy parameters of polystyrene. These improvements were more pronounced in the specimens with triphenyl phosphate and triphenyl phosphate-melamine cyanurate due to the synergistic combination of condensed phase action of nanoclays and gas phase actions of triphenyl phosphate and melamine cyanurate.