A simple amperometric alcohol sensor was developed using a cell membrane of acetic acid bacteria, a gas-permeable membrane and an oxygen electrode. The cell membrane of Gluconobacter suboxydans IFO 12528 was adsorbed on a nitrocellulose filter and attached to the Teflon membrane of the oxygen electrode and these membranes were then covered with the gas-permeable membrane (porous Teflon). When a sample solution containing ethanol was injected into the alcohol sensor system, the sensor current decreased markedly with time and reached a steady state after approximately 3 min. A linear relationship was observed between the decrease in current and the ethanol concentration up to 25 mg l–1. The sensor was found to have a good selectivity, which was better than that of an enzyme electrode with alcohol oxidase. The response of the sensor decreased at temperatures greater than 45 °C, and good responses were obtained over a period of 15 d. The sensor was applied to the determination of serum ethanol. There was a good correlation between the results obtained by the sensor and those obtained by gas chromatography (correlation coefficient r= 0.99). The current was reproducible with a relative error of ±6.2% when the ethanol concentration of the serum was 2.3 mg ml–1. The standard deviation was 0.07 mg ml–1 in nine experiments.