One of the important properties demanded for many textile fabrics is their flame resistance. This requirement concerns a wide variety of fabrics suitable for interior furnishings, especially public service buildings, means of transport, as well as for various technical applications. In order to fulfill these needs, a new process for making polyester fibres flame-retardant has been developed within a target project implemented jointly by 'ELENA' S.A. Works and the Institute of Textile Material Engineering. The process consists in incorporating into the chain of poly(ethylene terephthalate) an organo-phosphoric compound in a quantity sufficient to provide a phosphorus content in the polymer at a level of 0.55-0.57% by wt. Such a quantity of phosphorus brings about a considerable improvement in the resultant fibre flame resistance without any deterioration in the fibre processing behaviour. Good spinnability of the modified fibres makes it possible to produce a range of continuous filament yarns, both twisted and textured, converter tow and staple fibres. The results of tests obtained, according to Polish Standards, showed that the modified flame-retardant polyester yarns are suitable for the manufacture of a wide range of decorative fabrics satisfying the fire-safety requirements for use in public service buildings and means of transport. The fibres may be also used for various technical applications.