The adsorption of 4-chloroguaiacol (4CG) onto activated carbon prepared from the oil palm shell (OPSAC) was studied. The adsorbent was prepared from oil palm shell raw material impregnated in sodium hydroxide (NaOH) solution followed by the pyrolysis and activation process at 800 degrees C in N-2 and CO2 gas, separately. The effects of solution pH, agitation time, and initial concentration of 4CG were evaluated. 4CG adsorption uptake was found to increase with increase in contact time and initial concentration, while the high adsorption was obtained in an acidic medium at pH=2. The high Brunauer-Emmett-Teller (BET) surface area and the average pore diameter were equal to 2247 m(2)/g and 2.68 nm, respectively. The surface morphology and functional groups of the activated carbon were determined by using scanning electron microscopy and Fourier transform infrared analysis. The adsorption equilibrium data were analyzed by Langmuir, Freundlich, and Temkin isotherm models. Adsorption data of 4CG from the activated carbon were in agreement with Langmuir isotherm, with a maximum monolayer adsorption capacity of 454.45 mg/g. The applicability of two kinetic models, the pseudo-first-order and pseudo-second-order models, for describing the data was studied and the adsorption kinetics was found to follow the pseudo-second-order model. Oil palm shell-activated carbon was shown to be a capable adsorbent for removing a high percentage of the initial concentration of 4CG in aqueous solution at 30 degrees C. (C) 2010 Elsevier B.V. All rights reserved.