Batch experiments were performed to study the sorption behaviour of Ba2+ ion on three different clay minerals determined to be predominantly kaolinite, montmorillonite and mixed chlorite-illite. Synthetic groundwater was used and the concentration of Ba2+ ion was in the range of 10−8 to 10−4 N. Grain sizes of the solid particles were all <38 μm. Cation exchange capacities were obtained using the silver-thiourea (AgTU) method. The variation of RD values was studied as a function of contact time, shaking rate, Ba2+ ion concentration, v/m ratio and pH. The saturation time varied with each type of clay; about 6, 8 and 12 days of shaking time were necessary for chlorite-illite mixed clay, kaolinite and montmorillonite respectively. Shaking rate affected only the rate of sorption and not the saturaton RD values. Sorption was found to be reversible on kaolinite and partly reversible on montmorillonite and chlorite-illite clays. The variation of RD as a function of Ba2+ ion concentration exhibited characteristic inverse S-shaped curves suggesting the presence of at least two different types of exchange sites. Sorption of Ba2+ ion was observed to depend on pH and v/m ratio. The sorption isotherms were found to fit Freundlich and Dubinin-Radushkevich type isotherms well.