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The search for means and methods of raising the quality, improving the physicomechanical properties, and modifying large-tonnage polymers will expand the directions of use and ensure the reliability of polymer articles in conditions of prolonged use.Polyvinyl chloride (PVC) is one of the most widespread and practically important polymer products. One reason for the extremely rapid growth of PVC production is the possibility of easily and variously modifying it and the simplicity of processing it. The areas of application of PVC materials are constantly expanding and the requirements for it are increasing with the evolution of industrial progress.Almost all PVC-based plastics contain plasticizers which increase the elasticity and cold resistance of the material and also decrease its processing temperature. At the same time, this reduces its fireproofing characteristics -the oxygen index (OI) decreases from 47% for the initial PVC to 20% for PVC with a 50% plasticizer -dioctyl phosphate (DOP) content. Due to the presence of the plasticizer, PVC ignites easily and burns with emission a large amount of smoke and toxic compounds. Reducing the combustibility of plasticized PVC is a complex problem.Phosphorus-containing flame retardants (FR) [1], which inhibit thermooxidative degradation in the temperature range of initial intensive decomposition of the modified polymer, reduce the intensity of emission of combustible volatile products of degradation, and increase the carbonizability of the polymer, are used to reduce the combustibility of polymer materials.Previous studies [2] showed that amino-tris-methylenephosphonic acid ammonium salt (ASAMP) is very effective for fireproofing poly(ethylene terephthalate) materials. When added to the polymer in the amount of 25%, composites with a fire-resistance class of V-0 are obtained.According to the data from thermogravimetric analysis (Table 1), the temperature of the maximum rate of decomposition of ASAMP (323°C) coincides with the temperature range of decomposition of PVC. ASAMP can fulfill the function of a carbonized residue (CR) foaming agent due to liberation of NH 3 in decomposition at 300°C. In the deeper stages of pyrolysis, bulky cross-linked structures are formed. The formation of such structures increases the volume of the entire system and also increases its thermal stability. This formed the basis for investigating the possibility of using ASAMP for fireproofing a PVC composite with a 50% ASAMP content.