Biotransformation of sinesetin (1) by larvae of Spodoptera litura was investigated. Compound 1 was converted to a new flavonoid, (+)-5,7,3',4'-tetramethoxyflavone-6-O-beta-D-glucoside (4), and two known flavones, 4'-hydroxy-5,6,7,3'-tetramethoxyflavone (2) and 6-hydroxy-5,7,3',4'-tetramethoxyflavone (3). These structures were established by IR, HR-EI-MS, HR-FAB-MS, 1D NMR, and 2D NMR spectral studies. The results indicate that the metabolic reaction of compound 1 by larvae of S. litura proceeded along two pathways; the main pathway is demethylation at the C-6 position followed by glucosylation, and the minor pathway is demethylation at the C-4' position.