Three partially purified polysaccharides were extracted from Phellinus linteus mycelia using hot water, 1% (NH4)2C2O4, and 1.25M NaOH/0.05% NaBH4, and the extracts were named PL-W, PL-A, and, PL-N respectively. PL-N mainly comprised xylose and arabinose with a high molecular weight (Mw) and the highest carbohydrate and uronic acid contents. PL-W and PL-A were mainly composed of glucose with high and low Mw fractions in various ratios. All three polysaccharides existed as compact coils in aqueous solutions and exhibited strong scavenging capacity and antioxidant activities in a concentration-dependent manner. The polysaccharides also had high uronic acid and carbohydrate contents and strong antioxidant activities. The Mws, monosaccharide compositions, and chemical structures of the polysaccharides also affected their antioxidant activities. PL-A and PL-N had better antioxidant activities and could thus be developed as potential natural antioxidant agents for applications in food additives and biomedical industries.