The mushrooms of the genus Ganoderma are popular for their important biological activities, such as antioxidation, anti-inflammatory, antitumour, antiulcer, antiviral, etc. Ganoderma capense is one of the important members of this fungus family, which possesses potential pharmacological properties. There is a dearth of information on the biochemical constituents of G. capense. The present study aimed to isolate, purify, and characterize the structure of the polysaccharide obtained from the mycelia of G. capense. A novel water-soluble polysaccharide (GCP50-1) was obtained from the dried powder of submerged fermentation mycelia of G. capense by extraction with hot water and further successive purification through diethylaminoethyl (DEAE) Sepharose CL-6B and Sephadex G-75 column chromatography. The average molecular weight of the polymer was 1.5 × 10(4)Da determined by a high performance gel permeation chromatography (HPGPC), and its specific optical rotation was be [α]₂₅(D)=+170°. The structural feature of GCP50-1 was investigated by monosaccharide analysis, partial acid hydrolysis, methylation analysis, periodic acid oxidation, gas chromatography-mass spectrometry (GC-MS), Fourier transform-infrared spectroscopy (FT-IR), and nuclear magnetic resonance (NMR) spectroscopy. The results obtained from the analyses indicated that GCP50-1 was an α-D-glucan with the main backbone chain of (1→4)-α-D-glucopyranosyl residue interspersed with (1→4, 6)-α-D-glucopyranosyl residue and the side chain attached to the O-6 position with (1→)-α-D-glucopyranosyl residue. This was the first report on the detailed structure elucidation of this novel polysaccharide from G. capense mycelia powder.