A crystalline polyferric sulfate (PFS) adsorbent was synthesized by oxidizing and precipitating ferrous ions under atmosphere. The morphology, structure, composition and specific surface area (SSA) and adsorptive efficacy to As(Ⅲ) of the adsorbent were characterized by SEM/EDS and TEM images, XRD patterns, FT-IR spectra, BET SSA analyses and adsorption experiments. The adsorbent presents as morphology of near-spherical aggregate and good crystallinity. A small amount of goethite co-precipitated with PFS in the case of the initial ferrous concentration of 1 mol/L and increased the SSA of the aggregates. The absorbent with the largest SSA showed good adsorption to As(Ⅲ) and good filtering performance in the high As(Ⅲ)-content solution of 10-100 mg/L under acidic, neutral and alkaline conditions (pH 2.09-9.01), and its maximal adsorption capacity and adsorption efficiency were 7911 μg/g and 96% separately.