Antioxidant activity of Hydrophila auriculata leaf extract and silver nanoparticles (AgNPs) were carried out for proving its utility in free radical mediated diseases. The flower extract and silver nanoparticles were screened for in vitro antioxidant activity by oxygen radical scavenging such as DPPH, total antioxidant assay and superoxide radical scavenging activity at different concentrations. The antioxidant potential was found to be dose dependent. AgNPs possess probable antioxidant activity as compared with Hydrophila auriculata leaf extract and near to the standard. It is an obvious indication that the resulting activity of the AgNPs is not due to any capping agents, which are found in minute amounts but is due to the elemental silver.