We demonstrate the antibacterial activities of superparamagnetic Fe3O4 embedded porous ZnO nanocomposite (NC) against the Gram-positive, Staphylococcus aureus (S. aureus) and Gram-negative, Escherichia coli (E. coli) bacteria. The chemical interaction between Fe3O4 and ZnO in nanocomposite is evident from X-ray photoelectron spectroscopy (XI'S). The NC exhibits stronger antibacterial activity towards S. aureus than E. colt. Further, antibacterial activity is found to be strongly dependent on the concentration of NC and their incubation time. The Fe3O4-ZnO NC shows excellent heat activated killing of bacteria under AC magnetic field (ACMF) than normal heating. This novel method of killing bacterial pathogens can be a new approach towards the treatment of a variety of microbial infectious diseases. Furthermore, it can be used as highly efficient separable and reusable materials for inhibition of bacterial growth under magnetic field. (C) 2014 Elsevier B.V. All rights reserved.