To develope effective decontamination agent containing ammonium ion as an ion exchanger for urban surface, which contaminated with radionuclides, domestic smectite was used as a starting material. The agents were made by variation of smectite, hectorite, ammonium hydroxide and water contents. The optimal manufacturing composition was defined by this study, which was stable smectite suspension, with high shear thinning fluid for actual application and high wettability for effective decontamination performance.