In the recent years, a new class of materials, inorganic/polymeric hybrid adsorbents, stands out as being very effective in removing trace concentrations of arsenic from contaminated groundwater. The inorganic component, hydrated ferric oxide (HFO) particles, very selective toward both As(III) and As(V) species. is irreversibly dispersed within a polymeric support using a chemical/thermal treatment. The hybrid adsorbents discussed in this paper use strong base anion (SBA) exchange resins of various porosities as polymeric host material. The efficiency of the hybrid adsorbent materials depends on three factors: the amount of adsorbent component (HFO), its dispersion and the accessibility to the adsorbent surface of HFO particles. The purpose of this study is the characterization of the hybrid products with emphasizes on the localization of HFO deposits in the porous structure of the polymeric supports, and how this localization influences the adsorption efficiency. Critical analysis of data obtained by conventional physical methods used for the characterization of porous solids (low temperature adsorption of nitrogen isotherms, mercury intrusion porosimetry, and scanning electronic microscopy (SEM)) reveals the layered HFO deposition on the pore walls, an essential condition for the most efficient adsorbents. (c) 2008 Elsevier Ltd. All rights reserved.