Novel porous Fe3O4/CuI/PANI nanosheets were successfully synthesized by a facile in situ redox reaction at room temperature. Remarkably, the morphology and properties of the nanocomposites can be adjusted by changing the molar ratios of Cu2+/aniline. The porous nanocomposite sheets with the molar ratios of Cu2+/aniline at 1:1 exhibit excellent microwave absorption property, which display strong reflection loss over a wide frequency range that can be manipulated by the absorber thickness. The nanocomposites with a coating layer thickness of 2.8 mm exhibit a maximum absorption of -35.3 dB at 13.28 GHz, and show a bandwidth of 3.2 GHz (from frequency of 12.1-15.3 GHz) corresponding to reflection loss at -10 dB. The Fe3O4/CuI/PANI nanocomposites also show excellent hydrophobic property, which may result in stability enhancement of the porous Fe3O4/CuI/PANI nanosheets. Our findings pave a new way to design and prepare porous sheet-like microwave absorption materials based on polyaniline, inorganic semiconducting materials, and Fe3O4 microspheres. (C) 2014 Elsevier Ltd. All rights reserved.