The 6'-O-gallate derivative of (3S, 4S)-4-beta-D-glucopyranosyloxy-3-methyloctanoic acid was isolated for the first time from the wood of Sessile oak (Quercus petraea (Matt.) Liebl.) and shown to be a precursor of cis-beta-methyl-gamma-octalactone. The structure of this precursor was determined by HRFAB-MS, NMR, LCMS, and chiral analysis of the liberated (3S,4S)-beta-methyl-gamma-octalactone on a chiral fused silica capillary column. Optical rotation was shown to be identical to that of the same compound previously isolated from the wood of Platycarya strobilacea Sieb. et Zucc. by Tanaka and Kouno in 1996. Moreover, the 6'-O-gallate derivative of a threo-4-beta-D-glucopyranosyloxy-3-methyloctanoic acid was tentatively identified as a minor precursor of trans-beta-methyl-gamma-octalactone in the same wood of Sessile oak.