The aldehyde dehydrogenase activity of the cytoplasmatic extracts of a A cetobacter aceti strain used industrially in vinegar production is investigated. Two different culture media, based on ethanol or glucose, were used to compare the strain growth and activity. The kinetic constants of the enzymatic activity have been determined for extracts from the strain grown on ethanol. Finally, a study has been made of the spontaneous enzyme de-activation, which seems to fit a first order kinetic.