The natural mordenite was treated hydrothermally with NaOH solutions, either with or without fusion with NaOH powder as pretreatment. Zeolite Na-P and analcime were identified as the reacted products, depending on the reaction conditions. The zeolites were identified by X-raydiffraction, and their cation exchange capacity (CEC) was determined. Zeolite Na-P has higher CEC (338 meq/100g) contrasted with the mordenite (181 meq/100g). Further more, the uptakes of NH4+ onto the zeolites have also been investigated. The Na-P has faster exchange rate, higher exchange amounts and better regeneration ability. The ammonium removal efficiency for the Na-P is above 90% at the ammonium initial concentrations less than 150 mg NH4+/g. It seemed that Na-P was fit for the further treatment of waters polluted with ammonium.