The use of rice husk ash (RHA) as an adsorbent for the adsorption of humic acids from water was studied. Optimum conditions for humic acids adsorption were found in batch method as follows, 60 min equilibrium time and initial in the range of pH 3-4. In addition, RHA was functionalized with 3-aminopropyltriethoxysilane. Again, the adsorption behavior of the modified rice husk ash (RHA-NH2) was studied. Optimum conditions for humic acids adsorption were found to be 30 min equilibrium time and initial pH in the range of 3-4. The adsorption capacity of RHA-NH2 was higher than that of RHA. Experimental adsorption data fitted well with the Langmuir equation and the maximum adsorption capacity was 8.2 mg/g. at pH 6. The column method was also performed. The comparative adsorption efficiencies of RHA-NH2 and commercial activated carbons showed insignificant difference. The RHA-NH2 adsorbent was applied for humic acids removal from surface water. (C) 2010 Elsevier B.V. All rights reserved.