Chitosan/Montmorillonite nanocomposite films are layer-by-layer assembled over the surface of commercial unglazed wall ceramics to utilize as the separator of microbial fuel cells (MFCs). The oxygen diffusion coefficient of the ceramic is decreased to about one-sixth of the blank-ceramic by the addition of seven bi-layers of the nanocomposite and fairly remained unchanged with further layer increments. The lower oxygen diffusion rate of separator provides more anoxic conditions in the anode chamber and sidelong reactions are prohibited thereby. The electrochemical impedance spectra of MFCs are interpreted using the equivalent electrical circuit fitting. The ohmic resistance is notably decreased by deposition of up to ten bi-layers of the nanocomposite, but it is slightly increased afterward for MFCs with 13 and 15 bi-layers. The charge transfer impedances have the rather similar trends with the ohmic resistance and the MFC with seven bi-layers has the minimum charge transfer resistances for both the anode and cathode electrodes. The maximum power and current densities of 119.58 +/- 19.16 mW/m(2) and 869.44 +/- 27.49 mA/m(2) were obtained for the MFC with seven bi-layers of nanocomposite which are twice as much as the MFC with the blank-ceramic. The wastewater treatment efficiencies of MFCs are not significantly affected by deposition of nanocomposite films. (C) 2018 Elsevier Ltd. All rights reserved.