In the present study, a simple and eco-friendly chemical direction for the synthesis of zinc oxide (ZnO) nanoparticles using leaf extract of Astragalus membranaceus (AM) has been used. X-ray diffraction analysis revealed the wurtzite hexagonal structure of ZnO nanoparticles. The transmission electron microscopy results suggested that the ZnO nanopowders were approximately spherical in shape and their size were found to be 35-38 nm. The calculated average crystalline size decreases from 38.54 to 11.68 nm when AM extract content increased from 0.5 to 1.5 wt%. Fourier-transform infrared spectroscopy confirmed the presence of functional groups of both leaf extract and ZnO nanoparticles. The experimental results showed the advantage of addition of the AM extract for controlling particle size.