Abstarct: The reaction of 4-(4-aminophenyl)urazole with phetalic anhydride in mixture of pyridine and acetic acid (3:2) as a solvent led to the related amic acid. Amic acid was heated in the same solvent mixture to give 4-(4-phthalimidophenyl)-1,2,4-triazolidine-3,5-dione.The structure of this new compound was confirmed using infrared spectroscopy and nuclear magnetic resonance. 4-(4-phthalimidophenyl)-1,2,4-triazolidine-3,5-dione was polymerized with hexamethylene diisocyanate and tolylene diisocyanate to give new homopolyureas with inherent viscosities in a range of 0.21-0.26 dLg-1.The structure of these new homopolyureas were confirmed using infrared spectroscopy and element analysis data. 4-(4-Nitrophenyl)urazole was reacted with hexamethylene diisocyanate, isophorone diisocyanate and tolylene diisocyanate.The product was polymerized without separation in DMF (as a solvent) with 4-(4-phthalimidophenyl)-1,2,4-triazolidine-3,5-dione, to give new copolyureas with inherent viscosities in a range of 0.4-0.55 dLg-1.The structure of these new copolyureas were confirmed using infrared spectroscopy and element analysis data. Thermal gravimetery Analysis was performed for all of the new homopolyureas as well as copolyureas.