Abstract: The effects of addition of different concentrations of soybean oligosaccharides (SBOS) in marine sediment microbial fuel cells (MSMFCs) were explored.The amount of microbes attached to the surface of the anode was closely related to the concentration of SBOS.The amount of microbes in MSMFCs added 2 g of SBOS was the largest, reaching 9.310×10¹¹cfu/m² and the number of microbes in MSMFCs added 6 g of SBOS was the lowest, 7.680×10⁸ cfu/m².Electrochemical tests showed that the concentration of SBOS affected the electrochemical performance of the anode.The capacity and the anti-polarization performance of anodes in cells added 2 g of SBOS were the best, while the worst was that added 6 g of SBOS.The long-term output voltage showed that the high concentration of SBOS assisted to improve the output voltage of MSMFCs.The average output voltage of the cell added 6 g of SBOS was 45 m V higher than that of the blank group and 15~20 m V higher than those of other experimental groups.Heat loss of organic matters showed that the highest consumption rate was 66.15% of the blank group, and the lowest consumption rate was 50.63% of the group added 6 g of SBOS.Mechanism analysis showed that SBOS affected the electrochemical and the electrogenic performances and the organic matter consumption rates of MSMFCs by changing the number of microbes.