Bead cellulose loaded with iron oxyhydroxide (BCF) with 47 mass% Fe content was prepared and was successfully applied to the elimination of arsenic from aqueous solutions. A clearer understanding of the arsenic removal mechanism will provide accurate prediction of the arsenic adsorptive properties of the new adsorbent. To study the mechanism of the adsorption process, we measured the extended X-ray absorption fine structure (EXAFS) spectra of arsenite and arsenate sorbed onto the adsorbent with different surface coverages. Both arsenite and arsenate were strongly and specifically adsorbed by akaganéite adsorptive centers on BCF by an inner-sphere mechanism. There was no change in oxidation state following interaction between the arsenic species and the BCF surface. The dominant complex of arsenic species adsorbed on akaganéite was bidentate binuclear corner-sharing ((2)C) between As(V) tetrahedra (or As(III) pyramids) and adjacent edge-sharing FeO(6) octahedra. On the basis of the results from EXAFS spectra, the adsorptive characteristics of arsenic, such as the effects of pH and competing anions, were satisfactorily interpreted.