Electromagnetic interference shielding effectiveness (EMI SE) of multifunctional Fe3O4/carbon nanofiber composites in the X-band region (8.2-12.4 GHz) is studied. Here, we examine the contributing effects of various parameters such as Fe3O4 content, carbonization temperature and thickness on total shielding efficiency (SEtotal) of different samples. The maximum EMI SE of 67.9 dB is obtained for composite of 5 wt.% Fe3O4 (0.7 mm thick) with the dominant shielding by absorption (SEA) of electromagnetic radiation. The enhanced electromagnetic shielding performance of Fe3O4/carbon nanofiber composites is attributed to the increment of both magnetic and dielectric losses due to the incorporation of magnetite nanofiller (Fe3O4) in electrically conducting carbon nanofiber matrix as well as the specific nanofibrous structure of carbon nanofiber mats, which forms a higher aspect ratio structure with randomly aligned nanofibers. Furthermore, we prove that the addition of elastomeric polydimethylsiloxane (PDMS) as a coating for carbon nanofiber composite strengthens the composite structure without interfering with its electromagnetic shielding efficiency. (C) 2014 Elsevier Ltd. All rights reserved.