Carbon paste electrodes on which intact cells of Acetobacter aceti (IFO3284) are immobilized behind a dialysis membrane produce a catalytic current for the oxidation of ethanol in the presence of 2-methyl-5,6-dimethoxy benzoquinone (Q(0)) Analysis of the catalytic current reveals that the catalytic activity of the bacterial cells is due to alcohol dehydrogenase (ADH) existing in the cytoplasmic membranes. The membrane-bound ADH catalyzes the oxidation of ethanol by the use of Q(0) penetrating the membranes, in which Q(0) is reduced by accepting electrons from the enzyme. The reduced form of Q(0), in turn, reaches the electrode and is oxidized there. Thus, Q(0) serves as an electron transfer mediator between the intact cells and the electrode. The mediated bioelectrocatalysis behavior can be described by an equation of the catalytic current derived for an enzyme-based electrocatalysis. Performance of the electrode as an ethanol sensor is compared with that of an electrode modified with purified ADH. An ADH deficient strain and the ADH mutant harboring ADH gene are also examined as biocatalysts in place of A. aceti.