Adsorption isotherms of I-2 and malachite green (MG) by rice husk-based porous carbons (RHCs) from aqueous medium have been studied. Three samples of carbons prepared by NaOH-activation, three samples prepared by KOH-activation and two samples of commercial carbons have been studied. And the adsorption isotherms have been determined after modifying the carbon surfaces by oxidation with nitric acid and hydrogen peroxide and after degassing at 800 degreesC. The results have been found to follow the Freundlich adsorption isotherm. Three samples of N series have larger capacity for removing I-2 and MG from solution compared to that of the tested commercial carbons. The adsorption capacity of I-2 is Similar for K series and commercial carbons. And the capacity of commercial carbons for MG is larger than K series. The adsorption capacity of I-2 on oxidation carbons has increased for hydrogen peroxide treatment and decreased for nitric acid, and that of MG is decreased. But the adsorption capacities of I-2 and MG increase on degassing. On the other hand, the adsorption of I-2 increases after modifying the carbon surfaces by HCl without oxidation. Suitable mechanisms have been proposed. (C) 2003 Elsevier Science B.V. All rights reserved.