Nanoparticles are recognizing for their applications in various fields of medical sciences and they are also under safety concern. The effects of metals nanoparticles on environment is not yet completely known to us, but some of the study had been elaborated the toxic effects of metal nanoparticles to the environment both aquatic and terrestrial as well as human healths. So, eco-friendly green synthesized nanoparticles are now leading our interest for biosafety purpose. The aqueous solution of brown seaweed (Sargassum cinctum) had been utilized for green synthesized of Silver nanoparticles. The silver nanoparticles were formed due to the reduction of silver nitrate to aqueous silver ions in the presence of seaweed extract. The synthesized silver nanoparticles were characterized using UV-Visible Spectrophotometer, FTIR and Scanning Electron Microscopy. The biochemical compositions such as carbohydrates, proteins, lipids and starch were estimated for the mentioned species according to standard methods and the total phenol, in-vitro antioxidant activity and free radicals DPPH scavenging activities were also estimated. The phytotoxicity of green synthesized silver nanoparticles was evaluated by studying its effect on seed germination of Abelmoschus esculentus, one of the important vegetable items in Indian market.