This study considered the potential of a natural Australian zeolite, clinoptilolite, to remove ammonium from water. Ammonium-exchange capacity and rates of adsorption are critical to the assessment of the feasibility of the zeolite for application to continuous wastewater treatment. A laboratory study was undertaken, using pure solutions, to investigate the equilibria and kinetic characteristics of ammonium exchange in the zeolite. Binary equilibrium experiments provided information on the adsorption characteristics of the zeolite in terms of ammonia capacity at varying solution concentrations. These experiments also revealed that the highest ammonium removal efficiency was achieved when the zeolite＇s exchange sites were converted to the sodium form. Multicomponent equilibrium experiments were carried out to determine the effects of competing cations on the ammonium-exchange capacity of the zeolite. The laboratory study indicated the zeolite＇s selectivity for ammonium ions over other cations typically present in sewage (calcium, magnesium, and potassium), and provided information relevant to the design and operation of a continuous process.