The uptake of sodium, caesium and rubidium onto Los Trances clay was studied using the batch method. Sodium-22, rubidium-86 and caesium-137 were used as tracers. In most of the experiments cation concentrations used were 0.01 N. Triple distilled and deionized water ware used and the grain size of all solid particles was less than or equal to 53 mu m. In all cases a few hours of shaking was enough to reach the equilibrium. The ion exchange isotherm experiments were performed by using ammonium forms of the clays. Results showed that the ammonium form of Los Trancos clay was selective for Cs and Rb uptake but Na was not prefered. Cation uptake kinetics were complete in 1 h.