This study was conducted in order to analyze the ingredients and antioxidant activity of Suaeda japonica (turkey), which is abundantly present in Korea where mud flats are well formed due to the characteristics of halophytes. In the analysis of general composition, contents of carbohydrates, proteins, ash, and moisture were 10.7%, 8.3%, 7.6%, and 72.5% respectively. Among minerals, sodium was measured as 5.4%, which means that most ash was made of sodium. Heavy metal contents of lead, cadmium, arsenic, and mercury were 0.86 ppm, 0.04 ppm, 0.39 ppm, and 0.01 ppm, meaning Suaeda japonica satisfied standard food values. The 70% ethanol extract from Suaeda japonica was evaluated for its free radical scavenging activity and compared with a commercial antioxidant, BHA (butylated hydroxyanisole). As a result, the scavenging activities of hydroxyl radical, hydrogen peroxide, and xanthine oxidase of the extracts were equivalent to 30~50% of that of BHA.