To define the effect of the constituents of cask wood on commercial whiskey, ethanol-soluble extractives from mizunara (oak, Quercus mongolica Fischer var. grosseserrata Rehd. et Wils.) heartwood and commercial whiskey samples were studied. Compounds isolated from the oak heartwood, including beta-sitosterol(1), beta-sitosterol-beta-glucoside(II), (+)-dimethoxy-iso-lariciresinol (lyoniresinol, III), and alpha-D-glucose (IV), were detected in all of the commercial whiskey samples. Other compounds identified chromatographically among the oak heartwood extractives were syringic acid (V), gallic acid (VI), and dimethoxy-iso-lariciresinol-xyloside (lyoniside, VII). However, compounds V and VI, which have been reported in undiluted whiskey, were not detected in the commercial whiskey samples.