<p>A vermiculite clay mineral was applied as a column material of high performance liquid chromatography (HPLC) in order to eliminate radioactive Cs⁺ ions from contaminated water. A column was prepared by packing 2 g of vermiculite into a stainless tube of 0.6 cm (i.d.) × 5 cm (length). When an aqueous solution containing 0.1 mM of CsNO₃ and 1M of Mg(NO₃)₂ was passed through the tube, Cs⁺ ions were captured effectively until the flowed volume attained ca. 30 mL. Based on the results, it was estimated that the same column was capable of purifying 4.8 liter of water contaminated at the radioactive level of 3000 Bq/kg.</p>