Ammonia (NH₃) is not only a characteristic malodorous contaminant, but also one of the important precursors in the formation of haze. In engineering practice, the most widely used technology for NH₃ purification is adsorption, and the development of adsorbent with excellent NH₃ adsorption capacity is the key to adsorption method. Herein, the surface acidic sites of layered birnessite-type MnO₂ were regulated for the adsorption of NH₃. Results presented that the adsorption capacity of birnessite-type MnO₂ reinforced by surface acidic sites could reach 36.1 mg/g, which significantly superior to pristine MnO₂ and other commercial carbon materials. In addition, the effects of space velocity, NH₃ concentration, adsorption temperature and relative humidity on its adsorption performance were also studied. It was found that the effect of space velocity and relative humidity had no significant effect on the equilibrium NH₃ adsorption capacity; while the equilibrium adsorption capacity showed an increasing trend with the rise of NH₃ concentration and the decrease of adsorption temperature. Furthermore, the function of surface acidic sites, especially Lewis and Brønsted acidic sites, in the adsorption of birnessite-type MnO₂ for NH₃ was further revealed. On the one hand, the acidic site strengthening method of acid impregnation can significantly increase the specific surface area of birnessite-type MnO₂, which is beneficial for the physical adsorption of NH₃. Importantly, this acidic site strengthening method significantly enhances the number and intensity of surface acidic sites of birnessite-type MnO₂, especially the Brønsted acidic sites, which greatly promoted the adsorption of alkaline gas NH₃. Finally, the cyclic thermal regeneration performance at low temperatures was further studied. This work reports a strategy to improve NH₃ adsorption performance by enhancing acidic sites, and further reveals the functional role of surface acidic sites in NH₃ adsorption.