A marine brown alga, Sargassum polycystum, showed high‐chromium biosorption capacity in batch and column mode of operation. The biosorbent performance was strongly influenced by equilibrium solution pH, with pH 2 as optimal condition for Cr biosorption. Isotherm experiments revealed that S. polycystum possessed a maximum chromium uptake of 69.4 mg/g at pH 2. The pseudo‐second order model was found to describe the chromium kinetic biosorption data with high‐correlation coefficients compared with pseudo‐first order model. Various thermodynamic parameters, such as ΔG°, ΔH°, and ΔS°, were calculated, indicating that the present system was a spontaneous and endothermic process. A packed column was used to study the continuous chromium biosorption performance of S. polycystum. The biosorbent performance was evaluated at different bed heights (15–25 cm) and flow rates (5–15 mL/min). Favorable conditions for Cr biosorption were observed at the highest bed height (25 cm) and lowest flow rate (5 mL/min); at which the Cr uptake and percent removal were recorded as 29.1 mg/g and 63.3%, respectively. Mathematical modeling of column experimental data was performed, using nonlinear forms of the Thomas and modified‐dose‐response models; with the latter able to describe the breakthrough curves with high‐correlation coefficients. © 2010 American Institute of Chemical Engineers Environ Prog, 2010