The Geastrum saccatum a mushroom, native to Brazil, is produced under natural conditions in the unexplored reserve of Mata da Estrela-RN. This species has curative properties for eye infections and diseases such as asthma. The tissues of this mushroom contain carbohydrates, proteins, lipids, moisture and ashes in amounts of 42.3%, 37.05%, 9.01, 1.4% and 10.2%, respectively. An extract from this mushroom was characterized by chemical analyses and (13)C and (1)H NMR spectroscopy. It contains high amount of glucose and traces of galactose. The signal appearing at 103.5 ppm was assigned to C1 of beta-glucose. The signals observed between 20 and 40 ppm suggest the presence of a glucan-protein compound. This glucan inhibited the lipid peroxidation at the dose of 0.27 mg/mL (59.1%) and it can protect cells against oxidative stress by scavenging of the hydroxyl (77%) and superoxide (88.4%) radicals at 0.27 mg/mL. The glucan (30 mg/kg) reduces the polymorphonuclear cell migration (57.6%). The ear edema induced by croton oil was inhibited by glucan (60.4% at 10 mg/kg) and by its association with diclofenac (5 mg/kg) (89.2%) or L-NAME (60 mg/kg) (86.23%). Histological analyses of the ear edema induced by croton oil in the presence of glucan (10, 30 or 50 mg/kg) showed a reduced degree of the polymorphonuclear cell migration. We concluded that the glucan has antioxidant, and antiinflammatory properties as well as its antiinflammatory effect are mediated by inhibition of both nitric oxide synthase (NOS) and cyclooxygenase (COX).