Silver nanoparticles of mean size 16 nm were synthesized by inert gas condensation(IGC) method.Crystalline structure,morphology and nanoparticles size estimation were conducted by X-ray diffraction(XRD) and transmission electron microscopy (TEM).Antibacterial activity of these silver nanoparticles as a function of particles concentration against gram-negative bacterium Escherichia coli(E.coli) was carried out in liquid as well as solid growth media.Scanning electron microscopy(SEM) and TEM studies showed that silver nanoparticles after interaction with E.coli have adhered to and penetrated into the bacterial cells. Antibacterial properties of silver nanoparticles are attributed to their total surface area,as a larger surface to volume ratio of nanoparticles provides more efficient means for enhanced antibacterial activity. Silver nanoparticles of mean size 16 nm were synthesized by inert gas condensation (IGC) method. Crystallographic structure, morphology and nanoparticles size estimation were conducted by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Antibacterial activity of these silver nanoparticles as a function of particle concentration against gram-negative bacterium Escherichia coli (E. coli) was carried out in liquid as well as solid growth media. Scanning electron microscopy (SEM) and TEM studies showed that silver nanoparticles after interaction with E. coli adhered to and penetrated into the bacterial cells. Antibacterial properties of silver nanoparticles are attributed to their total surface area, as a larger surface to volume ratio of nanoparticles provides more efficient means for enhanced antibacterial activity.