There are many reports about the use of medicinal plants in traditional medicine, as well as the application of metal nanoparticles in various biomedical fields. The purpose of the present study is bio synthesize of silver nanoparticles, using the aqueous extract of Alisma Plantago-Aquatica L plant and to achieve optimal conditions for the synthesis of these nanoparticles. For this reason, the effect of different parameters such as pH, extract volume, concentration of silver nitrate solution, temperature and reaction time were studied and their optimal amount was determined. Then, the nanoparticles synthesized in optimum conditions, were evaluated (UV-Vis), X-ray diffraction (XRD), Field-Emission Scanning Electron Microscopy (FESEM), Transmission Electron Microscope (TEM) and Fourier-Transform Infrared spectroscopy (FTIR). Strong and width peak of the visible UV spectrophotometer, at 438 nm wavelength, showed the formation of silver nanoparticles. The X-ray diffraction pattern confirmed the formation of crystalline silver nanoparticles at a size of about 25 nm. The results of FESEM showed nanoparticle shape in a spherical and monodisperse, with a particle size range of 20 to 58 nm. The TEM analysis also yielded a nanoparticle size of about 20 nm. The results of the Fourier transform infrared spectroscopy (FTIR), indicate the involvement of hydroxyl, amine and carboxyl groups in the plant extract in the synthesis of silver nanoparticles. The results of this study showed that the"Alisma Plantago-Aquatica L." plant extract can be introduced as an appropriate, affordable and safe alternate in terms of green chemistry, instead of toxic and high-risk chemicals.