Dried fruits of Terminalia chebula (TF) have been used as herbal medicine for diverse symptoms, and antioxidant activity was known to be involved in its bioactivities. The aim of this study is to elucidate structure and evaluate antioxidant effects of active TF polysaccharide (TFP). TFP was prepared using hot water extraction and HP-20 resin treatment remarkably reduced levels of phenolics, and proteins in extracts. Neutral polysaccharide (TFP-a) isolated by IEC was homogenous α-Glc(p)-rich polysaccharide (over 70% of α-Glc, 534.9 kDa, PDI 1.36) with smooth, porous, and flake-like morphology assessed using HPGPC, HPLC monosaccharide composition, FT-IR, and SEM analysis. GC-MS linkage and 1D/2D NMR data comprehensively supported that backbone of TFP-a was (1→4)-α-Glc(p) with branch at C6/C2 in and terminal α-Glc(p). Side chains were composed of (1→4)-β-Gal(p) substituted, or terminated with α-Ara(f), β-GalUA(p), β-GalUA(p)-Me, and α-Rhm(p). These results suggested that TFP-a consisted of amylopectin backbone with complex side chains of (1→4)-β-galactan linked at C4 in α-Glc(p). Antioxidant activity assays revealed that TFP-a exhibited potent, and concentration-dependent antioxidant effects including DPPH, superoxide radical scavenging and reducing power activities. Taken together, TFP-a is amylopectin type polysaccharide, and has potential to be developed as a natural antioxidant. In the future, we will study about the structure-activity relationships, and the antioxidant mechanism of TFP-a in vivo.