The anode biofilm plays an important role in the microbial fuel cell (MFC) performance, which relies on the catalytic function of the anodic biofilm to transform the chemical energy into electricity energy. In this study, fumarate, as a kind of electron acceptor, is added into the anode system of MFC to figure out its effect on the biofilm formation of S. oneidensis MR-1. With fumarate addition, more bacteria are observed on the anode surface, and the power density has been promoted by 2.41 times than that without fumarate. Mechanism analysis shows that the fumarate addition could impair the secretion of riboflavin and inhibit the indirect electron transfer process, by finishing the respiration process with fumarate as electron acceptor, which promoted the bacteria proliferation and the anode biofilm formation. (C) 2017 Elsevier B.V. All rights reserved.