Abstract: In order to develop an efficient and inexpensive material for As(Ⅲ) removal from water, natural ferromanganese ore (NFM) was used as adsorbent. Kinetic, thermodynamic, isothermal adsorption and adsorption/desorption experiments were conducted to evaluate the adsorption performance of As(Ⅲ). The mechanism was analyzed by Fourier transform infrared spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, and the adsorption characteristics were compared with those of iron-manganese binary oxide (FMO), birnessite (Bir), and goethite (Goe). The results showed that NFM was mainly composed of manganese oxide and iron oxide, with a Fe-Mn molar ratio of 6∶1, the specific surface area of 280.4 m²/g, and a saturation adsorption capacity of 48.3 mg/g for As(Ⅲ). The Freundlich model and the pseudo-second order kinetic model could better fit the adsorption process of NFM. XPS and other characterization analyses indicated that the synergistic effect of adsorption and oxidation of NFM was the key factor for As(Ⅲ) removal. Among them, manganese oxides exhibited excellent oxidation of As(Ⅲ), while iron oxides had strong adsorption.