Hydrous manganese oxide (HMO) was synthesized and its adsorption properties with respect to Ba(II) ions investigated as a function of contact time, adsorptive concentration, temperature and pH, using a radiotracer technique. The adsorption equilibrium is achieved quickly in ca. 30 min and the steady state values of adsorption at various concentrations (10–2–10–7M) agree well with the classical Freundlich isotherm. The adsorption increases with increasing pH and reaches a maximum followed by a plateau over a fairly wide pH range. The temperature markedly affects the extent of adsorption and the process is thermodynamically found to be irreversible.