The subject of the present invention is a method for synthesis of nanocomposite ion exchanger with high selectivity of cesium and cobalt removal. Nanocomposite ion exchanger is based on silica which is covered with layer of potassium-nickel hexacyanoferrate and ethanolamine what results in very developed surface of the material. Synthesis method is based on coprecipitation of sodium silicate, potassium hexacyanoferrate alcohol solution, nickel nitrate alcohol solution and aqueous solution of amino alcohol, preferably ethanolamine with suphuric acid. Obtained material is dried according to the aprippriate procedure and grinded finally. This material shows also high thermal stability and resistance to ionizing radiation.