AbstractAn organic‐POMs nanoparticle of PMo9V3/CS was successfully synthesized from chitosan (CS) and H6PMo9V3O40 (PMo9V3) by immobilized method. After characterization, PMo9V3/CS hybrids were determined to possess dual enzyme properties similar to peroxidase and oxidase (KO3). PMo9V3/CS exhibited good kinetic activity towards H2O2 and could catalyze the decomposition of H2O2 to generate ⋅OH and reactive oxygen species respectively. It also showed stability in wide pH range between 3 to 8. Based on the high peroxidase‐mimetic and ROS activities, PMo9V3/CS for the first time was used as a nanomaterial to exhibit antibacterial properties against E. coli (gram negative bacterium). PMo9V3/CS‐based antibacterial showed high proficiency in damaging the existing biofilm and preventing formation of new biofilm than H2O2. This performance was a contribution of the CS‐mediated membrane destabilization and POM‐mediated oxidation of bacteria in the electron transport chain, causing the deformation of rod shape morphology and the decrease of density count of the bacteria. Therefore, PMo9V3/CS shows excellent antioxidant activity and enzymatic‐stability for clinic application.