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Polyester forms a major constituent among the synthetic fiber industry. It is the most popular synthetic fiber because of its high strength and esthetic appeal. Polyester being highly crystalline, hydrophobic and devoid of reactive groups, it is difficult to introduce reactive phosphorus into the fiber structure through chemical reactions with the phosphorus compounds. Fairly large quantities of the FR chemicals have to be incorporated to achieve self-extinguishing behavior. Although not all Flame Retardant (FR) chemicals are hazardous, it is advisable from an ecological point of view to introduce minimum quantities of FR substances in the fiber structure. The present Paper tries to address the said problems in a small way, so that the PET fiber could be better acceptable. Therefore, graft co-polymerization of nitrogenous vinyl monomers has been carried out on the fiber followed by its reaction with phosphorus chemicals, thereby incorporating reactive phosphorus in the grafted substrate. It has been shown that a very small amount of the FR chemical could impart fire resistance of very high order to polyester. Self-extinguishing characteristic was achieved for poly (ethylene terephthalate) fibers with acrylamide-grafted-phosphorylated (AM-g-P) PET fibers containing just 0.189 % phosphorus on-weight-of-fiber (owf). Similar results were obtained for methacrylamide-grafted-phosphorylated (MAm-g-P) polyester fibers at the 0.77 % phosphorus content level. Efficiency of phosphorus in presence of nitrogen that was achieved was at 263 % for acrylamide (AM) system, while it was –12 % for acrylonitrile (AN-phosphorus combination). This is attributed to P-N synergism in case of the FR polyester system when the nitrogen is in the amido form present in AM and MAm monomers