Abstract: In this study,antioxidant activities of polysaccharides(PL-N)isolated from Phellinus linteus mycelia were investigated. The chemical compositions and preliminary physicochemical properties of the PL-N were analyzed by physical and chemical methods. On this basis,the scavenging abilities on DPPH and hydroxyl free radicals,the protective effects on hydrogen peroxide-induced neurotoxicity in SH-SY5Y cells,and antioxidant activity in vivo of the PL-N were evaluated by using in vitro antioxidant trials,cell assay and D-galactose-induced aging mice models. The results showed that the carbohydrate and uronic acid contents of PL-N were 84.92% and 16.92%,respectively,and it had no proteins. PL-N was mainly composed of D-arabinose,D-xylose,D-glucose and D-galactose with the molar ratio of 5.5:7.8:1.8:1.0. PL-N exhibited prominent free-radical scavenging capacities and antioxidant activities in vitro in dose-dependent manners. At a concentration of 2.0 mg/mL,the scavenging effects of PL-N on DPPH and hydroxyl radicals were 72.1% and 83.3%,respectively. Meanwhile,the viability of oxidative damaged cells reached 88.7% after PL-N pretreatment at a concentration of 80 μg/mL,which revealed its outstanding antioxidant activity in vitro. Compared with the model group,the administration of high-dose of PL-N improved viscera indices of aging mice,enhanced the activity of antioxidant enzymes and total antioxidant capacity(P<0.01),and significantly reduced the content of malondiadehyde in the serum and liver of aging mice(P<0.01). Therefore,these findings implied that PL-N had prominent antioxidant activity and could be explored as a natural antioxidant for potentially used in functional foods or medicines.