Silver nanoparticles of different size and shape were synthesized using Ocimum tenuiflorum leaf extract. The nanoparticles were characterized by UV–visible, TEM, XRD and FTIR measurements. The toxicity of the silver nanoparticles was evaluated against zebra fish Danio rerio using direct exposure to silver nanoparticles and indirectly through food chain via feeding silver nanoparticles exposed chironomous larva) There was no toxicity developed against Ocimum tenuiflorum stabilized silver nanoparticles and it could penetrate all tissues including the brain through BBB Life time protection can be given to healthy young ones at a very low concentration (160ug) by simple bathing method.