Abstract: AimTo isolate polyphenols from grape seeds and to evaluate their antioxidant effects. MethodsPure compounds were isolated by using Diaion HP20, Toyopearl HW40 chromatography repeatedly, as well as semi-preparative RP-HPLC, from ethyl acetate extract of grape seeds. IR, MS, NMR, CD, X-Ray crystal diffraction spectral analysis were used to identify the structures. The antioxidant effects of different type of structures were screened by reducing power and DPPH (α,α-diphenyl-β-picrylhydrazyl)free radical scavenging tests. Then, SCGE (single cell gel-electrophoresis) technique was used to investigate the effects of these potent antioxidant phytochemicals on cellular DNA oxidative damage with mice spleen cells, damage was induced by H₂O₂. ResultsEleven compounds were obtained including 3 novel structures, viniferones A, B and C. Proanthocyanidin B4, catecin, epicatechin and gallic acid showed strong antioxidant power, and at lower concentration (10 μmol·L^-1, 25 μmol·L^-1), they can prevent cellular DNA damage, while 150 μmol·L^-1 catechin induced damage by itself. ConclusionViniferones A, B and C were reported for the first time. That polyphenols investigated were shown to be good cellular DNA oxidative damage-preventing phytochemicals at lower concentration, could be used to explain the nutrient effect of grape seed polyphenols at certain degree. At the same time, higher concentration of polyphenols can induce oxidative damage, suggesting that dose is one factor to determine the nutrient effects.