The present invention relates to fire-retarded compositions comprising, by weight, the total being 100 parts: 50 to 75 parts of a blend of a polyamide (A) and a polyolefin (B), 25 to 50 parts of a blend comprising: 0.1 to 48.8 parts of a fire retardant, 0.1 to 30 parts of a phosphorus-containing plasticizer, 0.1 to 10 parts of a zeolite, the total of these three products being between 25 and 50. These compositions have a V0 or V1 classification according to the UL94-VB test when a fire test is carried out on test specimens 1.6 mm in thickness. They have many advantages, in particular the elongation at break measured according to ISO R 527-1B exceeds 100%. As regards the impact strength, they have a non-brittle behaviour in multiaxial impact at room temperature according to ISO 6603-2 (at a rate of 7.7 m/s). They retain at least 50% of their mechanical properties after ageing for seven days at 120.degree. C. in hot air. These compositions are useful for insulating and protecting electrical cables and optical fibres and for moulding electrical cases and connectors.