In this study, an experimental design technique, the factorial design 3(3), has been used to investigate the biosorption of chromium(VI) from the aqueous solutions by the brown seaweed Sargassum muticum. The three factors considered were temperature, sorbent dosage and initial metal concentration at three markedly different levels. The biosorption of chromium(VI) by the algal biomass is highly pH dependent, favoring higher metal-ion removal at low pH. The S. muticum exhibited the higher Cr(VI) uptake capacity at pH 2. An empirical model was developed and validated applying ANOVA incorporating interaction effects of all parameters and optimized using response surface methodology. The optimization study indicates 84% as maximum removal at 50 C, 20 mg/L of metal concentration and a sorbent dosage of 2 g/L. At these optimal conditions, kinetics and isotherm models were obtained. The kinetics studies showed that the process of biosorption of Cr(VI) with S. muticum was been satisfactorily described by a process of chemical sorption of pseudo-second order. The experimental equilibrium data obtained have been analyzed using two-parameter isotherm models (Langmuir. Freundlich and Temkin). The most appropriate equation for describing the isotherm profiles was the Langmuir model. (C) 2011 Elsevier B.V. All rights reserved.