Abstract: Fucoidan,also called fucan,fucosan or sulfated fucan,refers to a type of polysaccharide which contains L-fucose and sulfate ester groups,and is mainly derived from brown seaweed.It has been widely used in medical and food industry for its various biological activities such as anticoagulant,antitumor,antioxidant and immunomodulatory activity.We summarized the research progress on the preparation of fucoidan and low weight molecular fucoidan.The structure,bioactivity and toxicity of fucoidan were also discussed.