Abstract: GL-PP-3A, an active polysaccharide peptide, was isolated and purified from Ganoderma lucidum, and then its structure was analyzed. Crude polysaccharide peptides were extracted from Ganoderma lucidum with hot water, precipitated with ethanol and then dialyzed from Ganoderma lucidum. Subsequently GL-PP-3A was isolated and purified from the crude polysaccharide peptides by fractional precipitation and chromatography of Bio-Gel P-10 column. The repetitive unit of GL-PP-3A was analyzed by high performance gel permeation chromatography (HPGPC), monosaccharide composition and methylation analysis, ¹H NMR and ¹³C NMR. GL-PP-3A is a heteropolysaccharide which is composed mainly of glucose (Glc), and also contains saccharide residues such as rhamnose (Rha), xylose (Xyl), mannose (Man) and galactose (Gal) and 17 kinds of amino acids. Its weight-average molecular weight (M_w) and number-average molecular weight (M_n) were 1.7×10⁴ and 1.1×10⁴, respectively, with the ratio of M_w/M_n (molecular weight distribution) being of 1.49. Its backbone chain is composed of 1,6-linked β-D-Glcp and 1,3-liked β-D-Glcp at a ratio of 2∶1. Some of 1,6-linked glucose residuals of the backbone chain are substituted at 2-O or 3-O, and there are 1 to 31,6-linked β-D-Galp or 1,3-linked α-D-Manp in the branched chains, the nonreducing ends of which consist mainly of β-D-Glcp and a few Rha.