An unusual water-soluble glucan was isolated from the fruiting bodies of Ganoderma resinaceum following alkaline extraction. Its structure was determined using NMR spectroscopy ( 13 C, 1 H, and 1 H (obs.), 13 C HMQC), methylation analysis, and controlled Smith degradation. It was a highly branched β-d-glucan containing a (1→3)-linked β-d-glucopyranosyl main chain, partially substituted at O-6, principally, by side chains of 4-O-substituted β-d-glucopyranosyl groups, on average to every two residues of the backbone.