Ethanol is the main byproduct of anaerobic H2-producing fermentation in Klebsiella oxytoca HP1. Two moles of NAD(P)H are consumed to yield one mole of ethanol that may decrease bacterial hydrogen production. In this article the adhE gene that codes for acetaldehyde dehydrogenase was disrupted for the first time. A homologous recombination vector pTA-Str was constructed in which the adhE gene was disrupted by inserting an aminoglycoside-3-adenyltransferase (aadA) gene. As expected, the vector includes the insertion 5-adhE-aadA-adhE-3. The amplified DNA fragment 5-adhE-aadA-adhE-3 from pTA-Str was transformed into K. Oxytoca HP1 and one recombinant was obtained. PCR analysis of the resulting genomic DNA indicated the appropriate deletion and insertion. Compared with the H2-production of wild type K. Oxytoca HP1, the hydrogen yield of the mutant increased by 16.07% and ethanol concentration decreased by 77.47%, suggesting that inactivation of the adhE gene in K. Oxytoca HP1 is a potential method for enhancing bacterial H2-production.