The antioxidative activity and active compounds of fennel seeds were studied. The water extract of fennel seeds had a strong inhibition effect on the oxidation of linoleic acid in a water-ethanol solution. Its activity being comparable to that of BHT. The methanol-soluble part of the water extract was fractionated by chromatography on a Sephadex LH-20 column, the strongly antioxidative fractions being purified by repeated chromatography to afford compounds. These compounds were identified as 4-O-β-D-glucosyl sinapyl alcohol, 4, 9-di-O-β-glucosyl alcohol and 4-β-glucosyloxy benzoic acid on the basis of their spectral data. The isolated compounds exhibited the antioxidative effect in comparison with the control.