The electron-attaching properties of polyphenolic compound resveratrol were studied in vacuo by means of dissociative electron attachment (DEA) spectroscopy and in silico using density functional theory calculations. The most intense fragments generated by DEA to isolated resveratrol at thermal electron energy are semiquinone anions and neutral hydrogen molecules. On the basis of the present experimental and theoretical data, a new molecular mechanism for the antioxidant activity of resveratrol is presented. It is suggested that the activity of resveratrol in living cells is driven by dissociative attachment of electrons "leaked" from the respiratory chain to this polyphenolic molecule, followed by the formation of the H-2 antioxidant species inside mitochondria and participation in rnitochondrial energy biogenesis.