The antioxidant activity of hot water extracts of various parts, the leaf, stem, and root of Synurus deltoides was evaluated by various antioxidant assays, including total phenolic content, 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging, hydroxyl radical (${cdot}OH$) scavenging, superoxide dismutase (SOD), and xanthine oxidase (XOI) activities. The various antioxidant activities were compared with the standard antioxidants such as L-ascorbic acid, $alpha$-tocopherol, and butylated hydroxyanisole (BHA). Among the different plant parts, stem has been found to possess the highest activity in all tested model systems, the activity decreased in the order stems>roots>leaves. These results indicate that stem extract could be used as potential source of natural antioxidant.