N ANOTECHNOLOGY, a highly promising discipline in science and technology, is the emerging and novel trend that will redesign the future of several existing know how which will change every aspect of our lives and leads to the generation of uniqueness in all the streams of technology. Biological synthesis of metal nanoparticles using microbes is gaining momentum due to the ecofriendly nature of the organisms which reduce toxic chemicals. Plant pathogenic fungi produce extracellular degradative enzymes that may be important in pathogenicity. Biosynthesis of silver nanoparticles was investigated using pathogenic Fusarium oxysporum f. sp. lycopersici and nonpathogenic strains of the same fungal species. These silver nanoparticles were characterized by means of UV–vis spectroscopy, transmission electron microscopy (TEM). UV–visible spectrum of the aqueous medium containing silver ion showed a peak at 420 nm corresponding to the Plasmon absorbance of silver nanoparticles. Transmission electron microscopy (TEM) micrograph showed formation of well-dispersed spherical silver nanoparticles with mean sizes 11.20 nm and 15.38 nm for pathogenic and nonpathogenic strains, respectively.