Fucoidan, a complex sulfated polysaccharide containing substantial percentages of L-fucose and sulfate ester groups, is a constituent of brown algae and some marine invertebrates. Besides L-fucose, it frequently contains D- xylose, D-galactose, D-mannose and D -glucuronic acid. Fucoidan has no determined molecular formula, and its structure built up mainly of (1 → 2)-linked, 4- O -sulfated fucopyranose residues has been generally accepted for fucoidan from L.aminaria Japonical / Undaria pinnatifida.