Abstarct: tetrabromophthalimido-1,2,4-triazolidine-3,5-dione was prepared via the reaction of tetrabromophthalic anhydride with one mole urazine in DMAc. The structures of the monomer were identified and confirmed by IR, 1H-NMR and 13C-NMR spectroscopies. This compound, which is a monomer, was then reacted with two moles of phenyl isocyanate and the structure of product as a model compound was identitied. The structure of the model compound was determined by IR, 1H-NMR spectra.The polymerization of the monomers with stoichiometric amount of various diisocyanates, hexamethylene¬ diisocyanate (HMDI), tolylene ¬diisocyanate (TDI), and isophorane diisocyanate (IPDI), led to new polymers, in high yields and inherent viscosities. These polymers were characterizd by using and 1H-NMR spectroscopies, viscometery and thermal gravimetric analysis (TGA/DTG).