In the present study we proposed a green approach for the synthesis of ZnO nano particles using Euphorbia hirta leaves extract. ZnO nanoparticles have a very broad range of applications especially as antimicrobial agent. There are various methods are available for the synthesis of ZnO nanoparticles but among them the synthesis of ZnO nanoparticles by using plant material is a very good alternative and eco friendly method. Leaves extract was used as a biological reducing agent for the synthesis of ZnO nano particles from the zinc nitrate. The prepared nano particles were characterized by using various analytical and spectroscopic tools such as UV visible spectroscopy, Fourier transform infrared spectroscopy (FT- IR), X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis. Along with this study we also investigate the antimicrobial activity of bio synthesized nanoparticles by using disc diffusion method against clinical and standard strains of Streptococcus mutans, Streptococcus aureus, Clostridium absonum, Escherichia coli and Arthogrophis cuboida, Aspergillius fumigates and Aspergillius nigar.