Abstract: The Ulva contains a variety of bioactive substances,the most important of it is the polysaccharide(ulvan)Ulvan,with special molecular structure,is a type of acidic polysaccharide located on the cell wall of green algae,and mainly composed of sulfated rhamnose,uronic acid and xylose. It can exert various biological functions by regulating cell signal transduction. Thus,Ulvan has gradually become a research hotspot in the fields of functional food and medicine. This article comprehensively reviews the recent research progress on the physicochemical properties,average molecular weight,monoscaccharide composition,chemical structure of Ulvan,and the biological activities,including anti-oxidation,immunomodulation,anti-tumor,hypolipidemic and anti-viral effects. Furthermore,the effects of the structure of Ulvan on the bioactivities are also introduced,to provide a reference for further development of the Ulva algae resources and utilization of the ulvan.