Chemical, derivatographic, IR spectral, and X-ray diffraction analyses were used to study thermal transformations in the system CO(NH 2 ) 2 3H 3 PO 4 and in the same system with addition of KNO 3 , CsNO 3 , LiNO 3 . 3H 2 O, and NH 4 NO 3 salts in the temperature range 20 3600oC. The influence of the chosen nitrate compounds on the process of reorganization of the constituent ingredients, evolution of nitrogen into the gas phase, yield of the solid residue, and preservation of nitrogen and phosphorus was revealed.Recently, nitrogen-phosphorus compounds have been widely used as cellulose modifiers and combustion inhibitors for various polymeric materials.The efficiency of nitrogen-phosphorus fire-retardants depends on the chemical nature of the nitrogen-containing component, degree of condensation of the phosphates used, ratio of the main components (nitrogen to phosphorus), additives introduced, and some other factors [137].It is known that the nature of the metal cation in inorganic additives present in nitrogen3phosphorus systems can strongly modify their fire-extinguishing properties and decomposition temperature [2,3]. For example, amidophosphate formulations are effective fire-protecting means. However, studies of the thermal decomposition of phosphorus-nitrogen mixtures and of the influence exerted by addition of inorganic salts on the structural-chemical transformations in the course of their heating are virtually not reflected in the literature at all. EXPERIMENTAL Systems composed of a mixture of phosphoric acid and carbamide, CO(NH 2 ) 2 3H 3 PO 4 (NP), at a mass ratio N : P = 1 : 2, and the same formulations with addition of NH 4 NO 3 , KNO 3 , LiNO 3 . 3H 2 O, and CsNO 3 (Table 1) were chosen for study.The NP systems were prepared by successive introduction of carbamide and appropriate nitrate salts into phosphoric acid. The content of nitrogen and phosphorus after thermal treatment was determined using procedures described in [8,9].The X-ray diffraction patterns of the samples studied were recorded with a monochromatic Cu K = radiation on an IRS-50M installation, and the IR spectra, on a Perkin-Elmer instrument by the sandwich technique [10] in a polyethylene film in the frequency range 400 33900 cm !1 . The course of the thermal decomposition process was recorded with an MOM Q-1000 derivatograph (Hungary), with temperature raised at a rate of 10 deg min !1 in the interval 20 3 600oC. In view of the fact that vigorous gas evolution with ejection of the samples under study from crucibles occurred on heating the NP system with nitrate additives, thermograms were only recorded for the additives introduced into the system.