Heavy metal and Al sorption capacities of Ca-loaded Sargassum fluitans biomass were studied by using equilibrium methodology. An evaluation of sorption performance and modeling in a two-metal system was carried out with a modified multi-component Langmuir isotherm. The maximum uptakes of Cr, Pb, Cu, Cd, Zn and Al calculated from the Langmuir isotherm were 1.74 mmol/g, 1.65 mmol/g, 1.61 mmol/g, 1.15 mmol/g, 0.81 mmol/g, and 2.95 mmol/g at pH 4.5, respectively. The interference of Al in heavy metal biosorptive uptakes was assessed by ‘cutting’ the three-dimensional uptake isotherm surfaces at constant second-metal final concentrations. The reduction of Pb, Cu, Zn, Cd and Cr uptakes at its final equilibrium concentrations of 1 mM at pH 4.5 was 78.4%, 82.7%, 85.1%, 89.8% and 51.2% in the presence of 1mM Al ion, respectively. The presence of Al ion greatly affected the uptake of all heavy metals tested except Cr.