A flavanol glycoside, glucodistylin (1) and three polyphenol derivatives, gallate (2), (+)-catechin (3) and (+)-gallocatechin (4) were isolated from an aqueous acetone extract of the bark of Quercus acutissima. Of these compounds, glucodistylin exhibited uncompetitive inhibitory activity against recombinant human aldose reductase with an $IC_{50}$ value of $7.2{mu}M$. Furthermore, glucodistylin inhibited sorbitol accumulation by 48.84% at $50{mu}M$. This flavonoid showed therapeutic potential in the prevention and treatment of diabetes-related complications.