Ammonium ion exchange behavior of synthetic zeolites, i.e., sodalite (SOD), rho zeolite (RHO), Linde type A zeolite (LTA), and faujasite zeolite (FAU), was investigated by changing the initial concentration of ammonium ions and reaction time. Ammonium ion exchange behavior was dependent on the open‐window sizes, the pore structures, and the cation exchange capacities of these zeolites. Regarding sodalite with Na+ ions (Na‐SOD), ammonium ion exchange did not completely occur at the equilibrium state because the open‐window size is smaller than the diameter of ammonium ions. Regarding RHO with Na+ and Cs+ ions (NaCs‐RHO), the larger cations, Cs+ ion, in the cages obstructed the ion exchange at the initial stage. However, the amount of exchanged ammonium ions gradually increased with increasing reaction time, finally achieving equilibrium. Regarding LTA with Na+ ions (Na‐LTA), the amount of exchanged ammonium ions decreased with increasing reaction time, and then reached plateau. It indicated that both the ion exchange on the α‐cages and physical adsorption on the β‐cages occurred at the initial stage, which was followed by the equilibrium state of ion exchange on the α‐cages. Regarding FAU with Na+ ions (Na‐FAU), no dependence on reaction time was observed, because the size of the open‐windows is large enough for ion exchange of ammonium ions. The Na‐FAU, which has the biggest open‐windows among these zeolites, showed the highest exchange capacity for ammonium ions, 3.20 mmol/g.