Cesium-exchanged A and X zeolites were loaded with cesium acetate species and thermally treated in orderto inhibit the mobility of exchangeable cesium cations. The proposed procedure seems to block the cavitieschannels avoiding the releasing of cesium cations under the leaching conditions. The cesium impregnatedspecies did not induce strong structural modifications if they are used in small amounts (0.2 meq/g zeolite),but they promote transformation toward cesium orthosilicate if they are loaded in amounts as high as 2 meq/gzeolite. This orthosilicate retains safely the cesium as it is a component of the lattice.