Ten tetrabrominated bisimides of which eight were novel were tested as flame-retardant additives. They were prepared from corresponding bisimides by the addition of bromine. Structural properties and related thermal characteristics of these brominated compounds were determined, Flame-retardant properties of tetrabrominated bisimides were tested on high-impact polystyrene, containing various amounts of brominated bisimides, according to ASTM-D-3801, "Standard Test Method for Measuring the Comparative Extinguishing Characteristics of Solid Plastics in a Vertical Position," and DIN-51960, "Testing of Organic Floor Coverings Assessment of Flammability." It was observed that tetrabrominated bisimides had improved flame resistance of high-impact polystyrene. In addition, thermoxidative stability of novel three bisimides, 04, 14, and 05, were compared with the others.