The present work deals with the ultrasound assisted green synthesis of iron oxide nano particle using Coriandrum sativum leaf extract as a reducing agent. The synthesized iron oxide nanoparticle was confirmed by UV spectra. The characterization was done to know more about morphology and size of the particle by SEM analysis which shows spherical particles with size ranging from 20 to 90nm. The antimicrobial activity of the leaf extract and the synthesized nanoparticles was studied against the pathogens Micrococcus luteus, Staphylococcus aureus and Aspergillus niger. The ultrasound assisted iron oxide nanoparticle shows higher scavenging activity and antimicrobial activity compared with iron oxide nanoparticle synthesized by magnetic stirrer and Coriandrum sativum leaf extract.