Oil palm fibre was used to prepare activated carbon using physiochemical activation method which consisted of potassium hydroxide (KOH) treatment and carbon dioxide (CO2) gasification. The effects of three preparation variables: the activation temperature, activation time and chemical impregnation (KOH:char) ratio on methylene blue (MB) uptake from aqueous solutions and activated carbon yield were investigated. Based on the central composite design (CCD), a quadratic model and a two factor interaction (2FI) model were respectively developed to correlate the preparation variables to the MB uptake and carbon yield. From the analysis of variance (ANOVA), the significant factor, on each experimental design response were identified. The optimum activated carbon prepared from oil palm was obtained by using activation temperature of 862 degrees C, activation time of 1 h and chemical impregnation ratio of 3.1. The optimum activated carbon showed MB uptake of 203.83 mg/g and activated carbon yield of 16.50%. The equilibrium data for adsorption of MB on the optimum activated carbon were well represented by the Langmuir isotherm, giving maximum monolayer adsorption capacity as high as 400 mg/g at 30 degrees C. (c) 2008 Elsevier B.V. All rights reserved.