Adsorption isotherms were determined experimentally for Cd(II) adsorption from aqueous solution onto natural and oxidized corncob in a batch adsorber. The adsorption capacity of natural corncob was increased 10.8 and 3.8 times when the corncob was oxidized with citric acid (CA) and nitric acid (NA), respectively. The Cd(II) ions were adsorbed mainly to the carboxylic sites since the adsorption capacity increased directly proportionally to the concentration of carboxylic sites in the corncob. The effect of the solution pH in the adsorption isotherm on natural and corncob modified with CA was assessed and it was observed that the adsorption capacity of Cd(II) on corncob depends considerably on the solution pH; Cd(II) was not adsorbed at pH less than 2 and the adsorption capacity was increased five times while the solution pH increased from 3 to 6. The adsorption of Cd(II) on corncob was reversible and the Cd(II) desorbed almost completely while reducing solution pH from 6 to 2. The adsorption capacity of natural and modified corncob was increased slightly by augmenting the temperature. By performing mass balances of ions, it was corroborated that the adsorption is mainly due to ion exchange. (C) 2005 Elsevier B.V. All rights reserved.