We studied the antioxidant activity of Suaedajaponica, found in Korean mud flats. A 70% ethanol extraction yielded 9.74%. The 70% ethanol extract was further fractionated with hexane, chloroform, ethyl acetate, butanol, and water. The water fraction resulted in the highest extraction yields, but the ethyl acetate fraction resulted in the highest total phenol content and also total flavonoid content. The antioxidative activity of the fractions was evaluated using several methods and compared to commercial antioxidants. The scavenging activities of the hydroxyl radical, hydrogen radical, hydrogen peroxide, and xanthine oxidase of the ethyl acetate fraction were equivalent to that of BHA. The scavenging activities of the hydroxyl radical, hydrogen peroxide, and xanthine oxidase of the ethanol extracts were approximately 80~90% of that of BHA.