The present work reports the preparation of activated carbon fiber (ACF) from Kenaf natural fibers. Taguchi experimental design method was used to optimize the preparation of ACF using K2HPO4. Optimized conditions were: carbonization at 300 degrees C, impregnation with 30% w/v K2HPO4 solution and activation at 700 degrees C for 2 h with the rate of achieving the activation temperature equal to 2 degrees C min(-1). The surface characteristics of the ACF prepared at optimized conditions were also studied using pore structure analysis, scanning electron microscopy (SEM) and Fourier transform infrared (FT-IR) spectroscopy. Pore structure analysis shows that micropores constitute the most of the porosity of the prepared ACF. The ability of the ACF prepared at optimized conditions to adsorb phenol and p-nitrophenol from aqueous solution was also investigated. The equilibrium data of phenol and p-nitrophenol adsorption on the prepared ACF were well fitted to the Langmuir isotherm. The maximum adsorption capacities of phenol and p-nitrophenol on the prepared ACF are 140.84 and 136.99 mg g(-1), respectively. The adsorption process follows the pseudo-first-order kinetic model. (C) 2009 Elsevier Ltd. All rights reserved.