Background: Marine Enteromorpha polysaccharides (EPPs) have been reported to present various physiological and bioactivities based on their specific chemical structures, such as monosaccharide compositions and glycosidic linkages. Scope and approach: However, the structure-activity relationship of Enteromorpha polysaccharides is mostly unknown. This review aims to provide a brief summary of structural, functional, and chemical characteristics of Enteromorpha polysaccharides. Key findings and conclusions: Modified Enteromorpha polysaccharides have several powerful bioactive functions. Sulfated EPPs with lower molecular weights were found to exhibit excellent immune-relevant and antioxidant activities. Carboxymethylated, hydroxamated, phthaloyl, and acetylated derivatives also showed significantly enhanced antioxidant and antibacterial activities as well as moisture absorbing capacities. EPPs were considered as novel natural agents, exhibiting outstanding druggable effects compared with ordinary drugs. However, the structure-function relationships of them are yet to be clearly established. The purpose of this overview is focusing on the current advances in the structural characterization, biological activities and mechanisms of action of Enteromorpha polysaccharides.