Abstract: Background and Objective: Heavy metal pollution represents a serious problem with dramatic, ecological and human health consequences. This study aimed to investigate the hexavalent chromium (Cr(VI)) biosorption capacity of protonated biomass of the brown seaweed Cystoseira tamariscifolia (C. tamariscifolia). Methodology: C. tamariscifolia was harvested from the Atlantic coast of Morocco. The Cr(VI) removal from aqueous solutions by algal biomass were studied in a batch mode. Langmuir and Freundlich adsorption isotherms were applied to fit the experimental data. Results: Experimental results indicated that biosorption of Cr(VI) was highly pH dependent, favoring higher chromium removal at very low pH values. Equilibrium data were well fitted by Langmuir isotherm model with a maximum Cr(VI) uptake capacity (Qmax) of 81.96 mg g–1. The kinetic models showed that biosorption process was perfectly described by a pseudo-second-order model. Conclusion: The protonated biomass of C. tamariscifolia seems to be a suitable low-cost biomaterial for removing hexavalent chromium from aqueous solutions.