In this paper, we report the Ca2+ and Mg2+ cation exchange activities of the synthesized Na-zeolite A, which was synthesized from Indonesian Bangka kaolin by hydrothermal method. The application of activated Na-zeolite A as water softener was studied. The objective of this research is to observe the activated Na-zeolite A as a water softening agent to remove simultaneously the Ca2+ and Mg2+ ions from water solution. In principle, activated zeolite-A can be used as a water softener using the ion exchange concept. Atomic absorption spectroscopy (AAS) technique was applied for quantitative analysis of the remaining cations content in water samples after treatment with activated Na-zeolite A as adsorbent for the removal of Ca2+ and Mg2+ ions. The adsorbent dosage of activated Na-zeolite A was varied in the range between 30 mg to 2 g and also the contact times were varied from 0 to 90 min. The highest removal efficiency of Ca2+ (95.97%) and Mg2+ (94.93%) from hard water were Na-zeolite A as adsorbent for Ca2+ and Mg2+ removal from water. These properties of the activated Na-zeolite A suggested that it is suitable and effectively used in hard water softening and detergent building for Ca2+ and Mg2+ removing.