Sulphur groups were introduced onto the cell surface of Undaria pinnatifida to increase the sorption capacity for lead ions. The total sulphur content of the cell approached 13.8% (w/w) through xanthation. Xanthate groups introduced onto the cell wall of Undaria pinnatifida enabled the biomass to adsorb lead ion three times more than the control and the sorption capacity approached 1000 mg lead g(-1). Increased affinity for lead ions was thought to be due to the fact that sulphur groups have the ability to make strong sulphur-metal complexes compared with that of the carboxyl group. The removal efficiencies of several metal ions were changed for various pH conditions. Since the removal order was; Cu2+ = Cd2+ = Pb2+ much greater than Ni2+ = Zn2+ > Co2+ much greater than Ca2+ > Mg2+, the selective adsorption for lead, cadmium and copper ions was possible.