Exopolysaccharides (ExPSs) and endopolysaccharides (EnPSs) were isolated from mycelia and culture medium of Agaricus brasiliensis. Four polysaccharide fractions (ExPS-1-2, ExPS-2, EnPS-1, and EnPS-2) were puri¬fied from ExPSs and EnPSs using diethylaminoethyl anion exchange and a Sephadex G-100 gel filtration column, respectively, and their physicochemical properties were analyzed and evaluated to determine antioxidant activity. The results showed that rhamnose and mannose were the main monosaccharides of the polysaccharide fractions. ExPS-2 and EnPS-2 were acidic polysaccharide fractions and showed higher scavenging effects on 1,1-diphenyl-2-picryl- hydrazyl and hydroxyl radicals, and had higher reducing power in the in vitro antioxidant assays. In addition, the malondialdehyde contents, the total antioxidant capacity, and the alanine transaminase activity were also assessed to determine the antiaging effects; ExPSs showed more antiaging effects compared with EnPSs. The results suggest that polysaccharides extracted from A. brasiliensis have significant potential as natural antioxidants and antiaging agents.