Ecological biosynthesis of nanoparticles (NPs) are gained much interest among researchers. In present investigation, iron nanoparticles were synthesized via green synthesis method using Halophila ovalis seagrass extract, having the capacity of reducing iron ions to iron nanoparticles. Synthesis nanoparticles was confirmed by UV-vis spectroscopy, Scanning electron microscope (SEM) with EDS anlysis, Distribution of the elements were characterized by Elemental mappling in SEM analysis. Antioxidant activities of synthesis nanoparticles were measured against 2,2-diphenyl-1-picryl-hydrazyl (DPPH), TAA and TAP.