Considering the promising application of microbial fuel cells (MFCs) in the wastewater treatment, the inherent solid particles in the wastewater may affect the MFC performance. In this paper, the effect of inert particle concentration on the operation of MFCs is investigated by adding silicon dioxide (SiO2) particles into the anolyte. The results show that the existing SiO2 particles in the anolyte result in a decreased active biomass and a reduced electrochemical activity of the biofilm. The anode ohmic resistance is almost the same for MFCs with various SiO2 particle concentrations in the anolyte, while an increase in the charge transfer resistance is observed. A small amount of inert particles have little influence on the MFC. However, when the MFC is operated with the anolyte containing more than 500 mg L-1 SiO2 particles, the performance decreases significantly due to the low electrochemical activity and high internal resistance of the anode. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.