The sorption capacities of Pb and Cd ions on the Ca-loaded Laminaria japonica biomass were studied using an equilibrium methodology. An evaluation of sorption performance and modeling in a two-metal system were carried out using the multicomponent Langmuir isotherm. The maximum uptake of Pb and Cd ions, calculated from the Langmuir isotherm, were 1.85 mmol/g and 1.39 mmol/g at pH 4.5, respectively. At pH 4.5, the Langmuir model gave the following affinity correlated coefficient: 21.2 for Pb and 1.58 for Cd. The interference of Pb in Cd biosorptive uptake was presented by 2-dimesional isotherms, which were obrained by 'slicing' the three-dimensional uptake isotherm surfaces at each Cd concentration. Equimolar final concentrations of Pb and Cd of 1 mM at pH 4.5, the uptakes of Pb and Cd, based on their pure system, were reduced to 86.2 and 25.2%, respectively. For heavy metal loaded-biomass, the ion exchange using Ca ion can last more than consecutive sorption-desorption cycles.