Abstract:The in vitro antioxidant activities of three distinct Exocarpium Citrulli polysaccharides（ECPs）obtained by the water extraction-alcohol precipitation method were compared. Three polysaccharides with different molecular weights，i.e.，ECP-1，ECP-2，and ECP-3，were separated by a DEAE-52 cellulose column and Sephadex G-200，and the relationship between the structure and activity was explored.Ion chromatography，infrared spectroscopy，scanning electron microscopy，Congo red test，and thermogravimetric analysis（TGA）were employed to analyze the polysaccharides.The results demonstrated that all the three macromolecular polysaccharides were water-soluble. ECP-3 had stronger activity for scavenging free radicals than the other two acidic polysaccharides，which may be associated with the fact that ECP-3 contained more uronic acids.