It was revealed that the dry powder yeast extract (YE) has the ability to act as a biocatalyst as well as a mediator in a biofuel cell. The yeast extract, from Nihon Pharmaceutical Co., Ltd., was used as a biocatalyst in an open air cathode biofuel cell containing phosphate buffer for glucose oxidation. The anode medium with only the YE showed an immediate activity by producing a current and delivering power depending on its concentration. By adding glucose to the anode medium, the anode potential decreased with time to -0.2 V vs. normal hydrogen electrode (NHE), and produced a higher power compared to that without glucose. The biofuel cell produced an open circuit voltage (OCV) as high as 1 V. (C) 2012, The Society for Biotechnology, Japan. All rights reserved.