The invention concerns flexible high thermomechanical stress-resistant and fire retardant halogen-free thermoplastic compositions, comprising a polyamide block-graft copolymer consisting of a trunk and on average at least one polyamide graft, wherein the grafts are bound to the trunk by the residues of an unsaturated monomer (X) having a function capable of reacting with a polyamide at the amine-terminal, the unsaturated monomer residues (X) being bound on the trunk by grafting or copolymerization from the double bond thereof. The invention is characterized in that the compositions comprise a mixture: 50 to 70 wt. % of polyamide block copolymer, 25 to 35 wt. % of a flame-retardant agent selected among ammonium phosphates, phosphinates, pyrophosphates, and polyphosphates, about 2 wt. % of zeolite, or hydrotalcitemolecular sieves. Said compositions are particularly useful for making electric cables, electric components, for molding electrotechnical housings, or for making coating layers or thermal protection sleeves for fluid transfer lines in the automotive industry.