Abstract: Alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH) are the key enzymes of ethanol oxidation and acetic acid production in Acetobacter pasteurianus.ADH and ALDH exhibited dynamic changes in acetic acid batch fermentation, and reached the peak after 36h with specific activities of 8.21U/mg and 2.52U/mg, respectively.Enzyme activity of ADH was always higher than that of ALDH in the whole fermentation process.The acetic acid production rate was high when the enzymes activities were high and vice versa.The effect of ethanol to the enzymes was studied:the two enzymes exhibited low activity when fermentation was performed in medium without ethanol, which was 0.38U/mg and 0.28U/mg, respectively. When performed in medium with 1% ³% (v/v) ethanol, the enzymes activities were enhanced, and then were inhibited when the ethanol concentration was further raised.The effect of initial acetic acid was also studied:when fermentation was carried out in medium without initial acetic acid, ALDH activity was low, and ADH activity was 3.3 times (36h) higher than ALDH at most. The existence of initial acetic acid shortened the fermentation time and increased the acetic acid production rate, the activity of ADH and ALDH was enhanced accordingly, and the highest ALDH activity reached 7.46U/mg.