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As(III) oxidation to As(V) is deemed necessary for better arsenic removal, and separation is still the optimal approach for water remediation from As(III). Herein, sulfite (SIV) was adopted to activate MnFe 2 O 4 for simultaneous oxidation and adsorption of As(III) in neutral water. The As(III) removal was more efficient than a peroxidation of As(III) followed by adsorption. The adsorption capacity of MnFe 2 O 4 /S(IV) for As(III) (26.257 mg g -1 ) was much higher than those of MnFe 2 O 4 alone for As(III) (9.491 mg g -1 ) and As(V) (9.142 mg g -1 ). The mechanistic study corroborated that intermediate Mn(III) was the dominant oxidant responsible for rapid oxidation of As(III), and the dual roles of S(IV) as a complexing ligand and a precursor of oxysulfur radicals accelerated the redox cycle of Mn(II)/Mn(III). Moreover, S(IV) enhanced arsenic adsorption by driving more production of monodentate complexes. As(III) can be effectively removed over a wide range of temperatures (283.15-313.15 K) and pH (3-10) with the optimal pH of 7. The effect of coexisting ions and reusability of MnFe 2 O 4 were also investigated. Especially, the superior performance of MnFe 2 O 4 /S(IV) for As(III) removal in various water matrixes may help develop new removal technologies based on active Mn(III) for the water decontamination from As(III)., (Copyright © 2020 Elsevier B.V. All rights reserved.)