A water soluble, (1 -->6)-branched, (1 -->4) linked D-glucan (LB-B1), [alpha](D)(21) = +174.2 degrees (c 0.87, H2O), was obtained from a hot-water extract of the sporoderm-broken spores of Ganoderma lucidun (Fr.) Karst by HPSEC, with 0.001 mol/L sodium hydroxide as the eluant, the molecular weight (Mw) of LB-B1 was estimated to be 9.3 x 10(3). From the results of total hydrolysis, methylation analysis, acetolysis and 1D, 2D-NMR experimentation, it was concluded that LB-B1 was composed of repeating units with the following structure: alpha -D-Glc(p)-(1 -->6)-alpha -D-Glc(p)-(1 -->6)-alpha -D-Glc(p) 1 down arrow 6 (-->4)-alpha -D-Glc(p)-(1 -->4)-alpha -D-Glc(p)-(1 -->4)-alpha -D-Glc(p)-(1 -->4)-alpha -D-Glc(p)-(1 -->4-)-alpha -D-Glc(p)-(1 -->)(n)