Substrate concentration has great influence on the electrical performance of a microbial fuel cell (MFC). In this study, date syrup with a high sugar content and diversified types of nutrients was used as a substrate in a dual-chambered MFC. The results obtained were compared with glucose as a conventional substrate for power generation. A pure culture of Saccharomyces cerevisiae was used as a biocatalyst in the anode chamber and potassium ferricyanide as an oxidizing agent in the cathode side. Maximum power density of 65 mW/m2 was obtained in an MFC operated with date syrup at an equivalent total carbohydrate content of 6 g/l. When the electron acceptor in the cathode side was replaced with potassium permanganate, power density was increased almost 2.5-fold and reached 234 mW/m2. The system was loaded with low to high concentrations of sugar (1–7, 10, 20 and 30 g/l). However, at high concentrations of substrates, an inverse relationship with the MFC electrical performance was observed, which was most probably due to substrate inhibition in the MFC. Substrate inhibition models were applied to investigate inhibition kinetic from an electrical point of view. Tessier, Aiba and Haldane as inhibition models were well fitted with experimental data (R2 = 0.98–0.99). The tested models revealed that the inhibitory effect for the substrate can be described in terms of model parameters. In order to evaluate the effect of the concentration of substrates on electrical performance, different inhibition concentrations were suggested by the models with respect to electrical responses achieved in the MFC. Copyright © 2012 John Wiley & Sons, Ltd.