[en] In this work the extraction of cesium is more particularly studied. This element is indeed present in all the nuclear plants. It is particularly known for its diffusion capacity through the solids. It is the reason why it is present in the effluents of decontamination. The aim of this work is then to implement an extraction process of cesium contained in this type of effluents. For the support material of the process, an organic/inorganic hybrid compound with polysaccharide and metallic oxide has been developed by a complex coacervating phenomenon (phase separation by charge effect). With the aim to improve the mechanical resistance of this obtained hydro-colloid and to avoid the loss of matter in the process, these particles are coated with a metallic oxide (titanium and the silicon oxide) synthesized by a sol-gel process. At first, a direct coating by mixture of polysaccharides particles and metallic precursors has been considered. In this case, the adhesion of silicon or titanium in the polymer is difficult. Pure nano-particles solutions are then obtained. In order to solve this problem, a coating in two times has been developed: at first, an alkylated metallic precursor is grafted on the polymer. Preferential growth germs for oxide are thus obtained. Then, there is impregnation with the solution of metallic precursor. The oxide growths around the grafted precursors in coating the hydro-colloid. The next studies will bear on the control of the coating porosity. (O.M.)