Abstract: Aqueous Methanol extracts of four seagrass species- namely Enhalus acoroides, Thalassia hemprichii,Halodule pinifolia and Syringodium isoetifolium collected from Gulf of Mannar Biosphere Reserve, South India were analysed using thin layer chromatography (TLC) followed by DPPH (2, 2-Diphenyl-1-picrylhydrazyl) technique and total phenolic content (Folin-Ciocalteu method). 25-75% of major seagrasses resolved by means of TLC were active ntioxidants. Halodule pinifolia showed a higher number of antioxidant constituents with strong activity (75%). The strength of antioxidant activity was shown to be stronger by the constituents of H. pinifolia, T. hemprichii and E.acoroides. The total phenolic content in these seagrass extracts was in the range of 0.2878-1.0807 mg tannic acidequivalent/g. The results suggested that seagrasses have strong antioxidant potential. Further studies are being carried out on the other species of seagrasses of different habitats in order to provide complete data of the antioxidant activity
and characterization of the principle antioxidant agents, which can be used to treat various oxidative stress-related diseases in plants.