Radioactive isotopes of cesium are among the most hazardous CBRN agents that can be released to the environment at accidental or intentional CBRN incidents. This contaminant easily introduces to food and potable water because of unique mobility of Cs+ ion in the environment. While other radionuclides, e.g., 60Co or 90Sr, can be separated easily due to their ability to form insoluble products with many anions, most of compounds of 137Cs and 134Cs are soluble and, therefore, highly mobile in aqueous media. The project is devoted to the development of a porous composite material for selective adsorption of cesium. This material will combine high binding ability of incorporated heteropolyacids that are soluble compounds with insolubility of the silica-based adsorbents.