We report Undaria pinnatifida as a potential biosorbent for lead removal. U. pinnatifida exhibited approximately 350 mg of lead uptake capacity per gram of dry biomass within a pH range of 3 to 4. The major cellular component of U. pinnatifida in lead binding was thought as alginic acid existing in the cell wall. U. pinnatifida adsorbed lead ion selectively over other alkaline metal ions such as K’, Na’, Mg-2’ and Ca-2’. It was confirmed by using instrumental analysis including EDX and XPS that U. pinnatifida adsorbed lead ions on the surface of itself.