Drug conjugated iron oxide magnetite (FeO) nanoparticles are of great interest in the field of biomedicine. In this study, vancomycin (Van) conjugated magnetite (FeO) nanoparticles were envisioned to capture and inhibit the growth of bacteria. Hydrophobic FeO nanoparticles were synthesized by using co-precipitation of ferrous (Fe) and ferric (Fe) ions following a surface modification step with oleic acid as stabilizers. Thereafter, a ligand exchange technique was employed to displace oleic acid with hydrophilic dopamine (DOPA) molecules which have a catechol group for anchoring to the iron oxide surface to prepare water dispersible nanoparticles. The surface of the resulting FeO/DOPA nanoparticles contains amino (-NH) groups that are conjugated with vancomycin a coupling reaction between the -NH group of dopamine and the -COOH group of vancomycin. The prepared vancomycin conjugated FeO/DOPA nanoparticles were named FeO/DOPA/Van and exhibited a magnetic response to an external magnetic field due to the presence of magnetite FeO in the core. The FeO/DOPA/Van nanoparticles showed bactericidal activity against both Gram positive () and and Gram-negative bacteria (. ). Maximum inhibition zones of 22 mm, 19 mm and 18 mm were found against , and respectively. Most importantly, the vancomycin conjugated nanoparticles were effectively bound to the cell wall of the bacteria, promoting bacterial separation and growth inhibition. Therefore, the prepared FeO/DOPA/Van nanoparticles can be promising for effective bacterial separation and killing in the dispersion media.