Fucoidin,mainly found in various species of brown seaweed extracellular matrix,is one kind of natural sulfated polysaccharides.In the past decades,fucoidin are widely used asactive ingredient in cosmetics,functional food,medicine,aquaculture and livestock feed supplements because of their antioxidant properties.This article summarizes the research advances on the molecular structure and antioxidant potential of fucoidan and its underlying antioxidant mechanism.