Ammonia is useful for the production of fertilizers and chemicals for modern technology, but its high toxicity and corrosiveness are harmful to the environment and human health. Here, we report the recyclable and tunable ammonia adsorption using a robust imidazolium-based MOF (JCM-1) that uptakes 5.7 mmol g^-1 of NH₃ at 298 K reversibly without structural deformation. Furthermore, a simple substitution of NO₃ ^- with Cl^- in a post-synthetic manner leads to an increase in the NH₃ uptake capacity of JCM-1(Cl^-) up to 7.2 mmol g^-1.