Three unsatd. compds. bearing resp. phosphate, aryl bromide and sulfenamide moieties were used as flame retardants (FR) for flax fabrics. Due to the presence of carbon-carbon double bonds, radiation-grafting was considered to covalently bond these FR onto fiber structure. Grafting efficiency and location of FR mols. were investigated by wt. measurements and SEM-EDX observations. Flammability and esp. self-extinguishment were assessed by thermogravimetric anal., pyrolysis-combustion flow calorimetry and a non-standardized fire test already used in previous studies. All FRs were able to diffuse into elementary fiber bulk. Nevertheless only the phosphonated monomer (noted FR-P) was significantly grafted onto flax. Self-extinguishment was obtained for fabrics contg. at least around 0.5 wt% of phosphorus. On the contrary the FR content of flax fibers after radiation-grafting procedure and washing was negligible for FR-S and FR-Br, evidencing that these mols. have not been grafted upon irradn. Moreover, the combination of these mols. prevents the radiation-grafting of other mols. which showed good grafting rate when used alone.