Micro/mesoporous activated carbon was oxidized and used either as received or after modification as a support for the deposition of iron oxyhydroxide. The prepared samples were applied as adsorbents of arsenate from water phase. The initial materials and those after adsorption were characterized using adsorption of nitrogen, -potentiometric titration, FTIR, EDX, XRD, AAS, and thermal analysis. The results obtained suggest that oxidation of the carbon support increases significantly the amount of iron oxyhydroxide species deposited on the surface and thus decreases their dispersions and the efficiency of arsenate immobilization in the carbon pore system. Iron hydroxyoxides react with arsenate forming salts. Moreover, a meso/microporous carbon surface contributes to changes in the toxicity of arsenic via reduction of As(V) to As(III). This is visible in the increased degree of carbon oxidation. (C) 2010 Elsevier B.V. All rights reserved.