Azadirachta indica (Neem ) is an important medicinal plant with proven strong antiseptic, antiviral, antifungal and antibacterial properties. The study here presents the antibacterial and QS (Quorum Sensing) inhibitory potential of biogenic Silver nanopaticles (AgNPs) from Azadirachta indica leaf extracts. The nanoparticles were synthesized using an aqueous extract of Azadirachta indica leaves and silver nitrate solution. The size, crystal structure, elemental composition and other physical properties of nanoparticles were determined using different microscopic and spectroscopic techniques. The average diameter of the nanoparticles was found to be between 20-43 nm with crystalline morphology. These extracellularly synthesized AgNPs strongly inhibited Gram negative pathogenic species and exhibited demonstrable anti- Quorum Sensing (QS) activity as evident from pigment inhibition and 75- 80% decrease in biofilm mass on AgNPs treatment in a dose dependent manner.