The adsorption of hexavalent chromium from aqueous medium by rice husk-based activated carbon (RHC) was studied. The extent of adsorption was studied as a function of pH, contact time, contact temperature, adsorbate concentration and adsorbent with different pore structure. The removal of Cr(VI) by RHC was first introduced. The adsorption of two carbons activated by KOH-activation and NaOH-activation was discussed. The difference was studied through pore size distribution, pore volume and the adsorption capacity. (C) 2002 Elsevier Science B.V. All rights reserved.