A novel polysaccharide (LCP50S-2) with antioxidant activity was isolated from Litchi chinensis Sonn. The structure of LCP50S-2 was elucidated on the basis of physicochemical and instrumental analyses, and its average molecular weight was determined by gel permeation chromatography to be 2.19 × 10(2) kDa. The backbone of LCP50S-2 was composed of (1→3)-linked β-L-rhamnopyranosyl residues, (1→4)-linked α-D-xylopyranosyl residues, (1→4)-linked β-D-glucopyranosyl residues, and (1→4)-linked α-D-glucopyranosyl residues which branched at O-6. The two branches consisted of α-L-arabinopyranosyl residues and (1→6)-linked β-D-galactopyranosyl residues terminated with α-L-arabinopyranosyl residues, respectively. In the in vitro antioxidant assay, LCP50S-2 was found to possess DPPH radical-scavenging activity and hydroxyl radical-scavenging activity with IC(50) values of 220 and 266 μg/mL, respectively.