One new flavonol glycoside, patuletin-7-Ο-[6-Ο-caffeoyl-2-Ο-[(S)-3-hydroxyisobutanoyl]glucopyranoside] (astermaritimoside) (1) and four known flavonoids, patuletin-7-Ο-β-[-6-Ο-[(S)-3-hydroxyisobutanoyl]glucopyranoside] (2), patuletin-7-Ο-[6-Ο-caffeoylglucopyranoside] (3), patuletin-7-Ο-β-D- glucopyranoside (4) and quercetin-3-Ο-β-rutinoside (5) have been isolated from Asteriscus maritinus (L.) Less. Chemical structures were elucidated by mass spectrometric, and ¹H NMR, ¹³C NMR, COSY, HMQC and HMBC spectroscopic techniques. The antioxidative effect was evaluated using an electronic spin resonance (ESR) method in order to visualize the inhibition of the DPPH radical. The n-butanol fraction was found to possess a remarkable antioxidant activity that was correlated with the total amount of phenolics. The isolated compounds exhibited good antioxidant activity.