Rumen microbial fuel cells (RMFCs) are a promising technology for sustainable production of alternative energy and fiber waste treatment. However, the influence of catholytes with different oxidizing powers on anode metabolites and electrical properties of straw-fed MFCs will be mainly evaluated in this study. Furthermore, the exploration of nonlinear features in RMFCs would be another subject of debate. Results show that voltage generation correlates positively to anode total volatile fatty acids, acetic acid, and butyric acid concentrations, along with the ratio of acetic acid to propionic acid, which would favor the production of reducing equivalents. In addition, the finding of an attractor indicates that RMFCs possessing a chaotic characteristic is a nonlinear system and could be used to strengthen the metabolism of microorganisms. These observations will provide information for improvement in RMFC fed native plant fiber substrate. (C) 2013 Elsevier Ltd. All rights reserved.