Abstract: Moisture absorption and moisture retention of Mactra Veneriformis polysaccharide were investigated under two kinds of humidity conditions with hyaluronic acid as a reference. The result showed that polysaccharide had a certain degree of moisture absorption and long lasting moisture retention, and a certain degree of humidity-dependent. Taking VCas a referential substance, hydroxyl radical scavenging ability, DPPH scavenging ability and reducing capacity of Mactra veneriformis polysaccharide were studied. The result showed that it had a certain degree of antioxidant capacity, especially the capacity of scavenging the hydroxyl radical. These results clearly established the possibility that Mactra Veneriformis polysaccharide could be effectively employed as type of natural moisturizer and antioxidant.