The sorption of heavy metals (lead, copper, and cadmium) by a marine algal biomass Sargassum sp. was studied in single and multiple metal-ion systems. Kinetic experiments in the single-metal system revealed very rapid removal rates of metal ions, with ∼90% of the total adsorption occurring within 10-60 min. Biosorption performance for each single metal ion showed an increase in specific metal uptake with an increase in pH. Experimental data for each metal ion were well-described by the Langmuir adsorption isotherm. Generally, the algal biomass demonstrated the highest uptake for lead, followed by copper and cadmium, with this uptake trend correlating with the electronegativities and stability constants of the metal-ion hydroxides. The effect of the presence of multiple metal ions on the biosorption performance has been investigated, and the results have been evaluated using the modified competitive Langmuir model and modified Jain-Snoeyink model, both of which fit the data well. The metals with the highest uptake capacity in single-metal systems showed a greater inhibitory effect on the biosorption of other metal ions in the multiple-component systems. The study showed the good performance of metal uptake by Sargassum in both single- and multiple-metal systems.