Morchella esculenta, an edible medicinal mushroom native to China, is recognized as an unparalleled resource of healthy foods and drug discovery. This study firstly investigated the antioxidant activity of Morchella esculenta extracellular polysaccharides (MEEP). An in vitro antioxidant assay showed that MEEP exhibited strong hydroxyl radical scavenging activity and moderate 1,1-diphenyl-2-picryldydrazyl radical scavenging activity and reductive power. For antioxidant testing in vivo, MEEP were orally administered over a period of 60 days in a d-galactose induced aged mice model. Administration of the polysaccharides inhibited significantly the formation of malondialdehyde livers and serums, and raised the activities of antioxidant enzymes and the total antioxidant capacity in a dose-dependent manner. Furthermore, we also observed that MEEPs markedly enhanced the body's immune system by measuring macrophage phagocytosis and splenocyte proliferation in d-galactose induced mice. These findings suggest that EPs from Morchella esculenta are a promising source of natural antioxidants and immunoenhancing drugs.