In this paper, an alkali-soluble polysaccharide DIPs-3 was extracted with 5% NaOH/0.05% NaBH4 from the fruiting of Dictyophora indusiata. The structure of DIPs-3 was investigated by a combination of chemical and instrumental analysis. The monosaccharide composition analysis showed that DIPs-3 consisted of glucose only. Structural analysis revealed that DIPs-3 had a backbone of (1→6)-linked β-D-Glcp with substitutes at O-4 of Glcp residues. The branches were composed of terminal β-D-Glcp. Congo red analysis and dynamic rheology experiments indicated that DIPs-3 was a triple helical polysaccharide. The results of antioxidant activities showed that DIPs-3 exhibited high DPPH radical, ABTS radical and hydroxyl radical scavenging activities. It was suggested that DIPs-3 could be used as a potential natural antioxidant in food industry.