In the present report, simple and green protocols for the synthesis of ZnO nanoparticles under ambient conditions from the aqueous extracts of Murraya koenigii seeds were reported. The synthesized nanoparticles are characterized by UV spectrometer, FT-IR spectroscopy, powder XRD pattern, scanning electron microscope (SEM) and transmission electron microscopy (TEM) analysis. The synthesized ZnO nanoparticles tested for antimicrobial activities by Bauer-Kirby method using human pathogenic bacterial and fungal species. The synthesized nanoparticles exhibited good antimicrobial agent for all the four bacterial and three fungal species.