Nanotechnology is now creating a growing sense of excitement in the field of life science. Nano particles can be synthesized by physical and chemical method but green synthesis method is the most emerging approach of preparation due to eco friendly and less time consuming procedure. This study aimed at green synthesis, characterization and evaluation of antibacterial effect of nano silver on mastitis causing bacteria. Aqueous coriander leaf extract with certain concentration of reducing agent were used for the production of silver nano particles.