The removal of NH4+ on protonated layered perovskite oxide HCa2Nb3O10 center dot 1.5H(2)O from-an aqueous solution at room temperature using a batch method was investigated. The protons situated between the layers of the material are exchangeable with cations in solution. Distribution coefficient values, K-d (cm(3)/g), of Na+, K+, and NH4+ cations at pH 2.2 from a mixed solution (NaCl, KCl, and NH4Cl) containing 1.0 mmol/dm(3) of each ion were 1600 for K+; 2200 for Na+, and 10 500 for NH4+. The effect of solution pH on the ion exchange in aqueous solution (NH4Cl + HCl or NH4OH) showed a maximum uptake of 34 mg of NH4/g at around pH 6. The results indicate that the material is very effective for removing NH4+ at concentrations of less than 10 mg of NH4/dm(3).