The activation mechanism of typical bentonite powder with sulfuric acid was studied from variations in their surface area during the reaction. The surface area of activated samples at different activation temperatures and times were measured by methylene blue adsorption to quantify the effect of acid. The influence of activation time was investigated by isothermal experiments, performed at different temperatures. The specific surface area-time data were analyzed by using a modified kinetic model and the values of kinetic parameters were calculated. Also, the influence of acid concentrations on kinetic parameters was evaluated. The validity of proposed model to describe the bentonite activation kinetic was substantiated by computation of reaction time to achieve maximum value of specific surface area in other temperatures. (C) 2007 Elsevier B.V. All rights reserved.