Abstract: Fucoidan mainly derived from brown algae,is a water-soluble heteropolysaccharide containing sulfate groups. Fucoidan had a wide range of applications in medicine,health products,functional foods and other fields. The structure of fucoidan was complex,and the amount of sulfate groups had some influence on its biological activities. In this paper,the complex structure was outlined and some biological activities of it such as antioxidant activity, antiviral activity, antitumor activity, biological activity of α- glucosidase inhibition were introduced.