Zinc ferrite (ZnFe2O4) nanoparticles were prepared using a bio-mediated, environmental friendly and a less expensive route using Phyllanthus acidus as fuel. The nanoparticles were examined by Powder X-ray diffraction and Scanning Electron Microscopy techniques. The scanning electron micrographs of the synthesized ZnFe2O4 nanoparticles synthesized by this plant based method demonstrates irregularly shaped thin flakes of crystallites, showing voids and pores due to the escaping gases during the process. The synthesized nanoparticles were found to be in the range 11-20 nm. The antimicrobial activity was observed by the zone of inhibition induced by the plant mediated synthesis of the ferrite nanoparticles.