Three water-soluble glucans (PELPS-A1, PELPS-A2, and PELPS-A3) purified from the hot water extract of the basidiomata of an edible mushroom Pleurotus eryngii var. elaeoselini by chromatography on DEAE-cellulose 32 and Sephadex G-100 column were found to consist of only D-glucose as monosaccharide constituent. Structural investigation was carried out by acid hydrolysis, periodate oxidation, and NMR experiments (1H-NMR, 13C-NMR, DQF-COSY, TOCSY, ROESY, HMQC, and HMBC). On the basis of these experiments, the structures of the repeating unit of the three isolated polysaccharides were established as follows: (1) PELPS-A1: {[→3)-α-D-Glcp-(1→]3→4)-α-D-Glcp-(1→2)-α-D-Glcp-(1→6)-α-D-Glcp-(1[→6)-β-D-Glcp-(1→]2}n 6 ↑ 1 α-D-Glcp (2) PELPS-A2: [→6)-β-D-Glcp-(1→6)-β-D-Glcp-(1→6)-β-D-Glcp-(1→]n 3 ↑ 1 β-D-Glcp (3) PELPS-A3: [→6)-α-D-Glcp-(1→6)-α-D-Glcp-(1→6)-α-D-Glcp-(1→]n The dried basidiomata of P. eryngii var. elaoselini were tested for their antioxidant activity by DPPH and hydroxyl radical scavenging assays. The crude extract has shown a SC50 of 1.4 mg/mL for DPPH test while a SC50 of 5.7 mg/mL was observed for hydroxyl radical scavenging activity test. The antioxidant activity of PELPS-A1, PELPS-A2, and PELPS-A3, evaluated as hydroxyl radical scavenging activity, was similar and significant, suggesting their use as antioxidants.