Three-dimensional (3D) carbon nanofibers (CNFs) produced from pyrolysis of bacterial cellulose (BC) were used as the substrate for anchoring Fe3O4 nanoparticles. In order to control the dispersion of Fe3O4 nanoparticles on the surfaces of BC-derived CNFs (BC-CNFs), BC-CNFs were surface-treated in HNO3 solution. The resultant BC-CNF/Fe3O4 nanocomposites possessed ultra-small and highly dispersed Fe3O4 nanoparticles and demonstrated greatly enhanced absorption over their untreated counterparts. Moreover, among all BC-CNF/Fe3O4 nanocomposites, the BC-CNF/Fe3O4 containing 52.7 wt% Fe3O4 exhibited excellent absorption performance with the minimal reflection loss (RL) of -62.1 dB at 9.12 GHz, which is the best among all relevant CNF-Fe3O4 composites reported so far. (C) 2017 Elsevier B.V. All rights reserved.