Background and Objective: Development of methods without using plotant and poisonous material and minimum wastes to produce under control nano structures is of nanotechnologist concerns. In this way biologists, by previous knowledge, nano-scale minerals controlled making by microorganism, seeking organism capable making non-organic nanoparticles. The aim of this study is the extracellular production of silver nanoparticles with maximum dimention of 20 nm by Fusarium oxysporum fungi.Materials and methods: After studies to optimize growth condition, Fusarium oxysporum biomass in a medium containing yeast and malt extract is reproduced. After silver nanoparticles production in silver nitrate solution, this nanoparticles are studied by UV-Visible Spectrophotometry and Transmission Electron Microscopy (TEM) methods.Results: Studies showed that when Fusarium oxysporum biomass is put in 10-3 M of silver ions, can produce silver nanoparticles in the form of extracellular.Conclusion: Because of physical and chemical particular properties of silver nanoparticles with maximum diameter of 20 nm of Fusarium oxysporum fungi, its industrial production and applied evaluation is offered.