The use of natural reinforcements in composite materials has considerably increased due to numerous advantages. However, some drawbacks limit their industrial applications such as their hydrophilic character, their low thermal stability and also their flammability. Among different strategies to functionalize natural fibers, the radiation grafting appears promising. In this work, it was used to improve the flame retardancy and the hydrophobicity of flax fabrics. As an example, the procedure to radiation-graft phosphorus compounds on flax fabrics is presented. The influence of various experimental conditions on the grafting efficiency was assessed.It is possible to control precisely the grafting efficiency and the location of phosphorus in order to achieve the desired level of flame retardancy. Self-extinguishing behavior of fabrics can be achieved [1]. Hydrophobic fibers were also prepared according to similar procedure. This work is partly included in the French project called BIONICOMP, headed by IONISOS, with a consortium gathering of academic and industrial partners, in order to improve the performances of composites reinforced by natural fibers fabrics.