Potassium cyanide (KCN) is an inhibitor that reduces the activity of terminal oxidases in electron transport system of Klebsiella oxytoca. Previous research verified that K. oxytoca could induce cyanide-resistant respiration pathway when cells were grown in KCN condition. To address the role of cyanide-resistant pathway in regulating the respiration of bacterium in KCN incubation, 8-hydroxyquinoline (8-HQ), an inhibitor of cyanide-resistant pathway, was added to the bacterial suspension pretreated with KCN. This experiment was devised into 4 groups as below: (1). TSB (without KCN or 8-HQ), (2). TSB + 1 mM KCN, (3). TSB + 100 £gM 8-HQ, and (4). TSB + 1 mM KCN+ 100 £gM 8-HQ. Our results show 100 £gM 8-HQ exerted it slight toxicity to bacterial growth. However, the bacterial growth was severely impaired when the cells treated with KCN and 8-HQ concurrently as evidenced by the lower oxygen uptake rate of cells in comparison with the control group (without addition of 8-HQ). Furthermore, K. oxytoca grown in growth medium containing 100 £gM 8-HQ produced more significant H2O2. Thus we suggested that cyanide-resistant respiration of K. oxytoca could protect the cells from H2O2 damage. Since cytochrome d has been implicated in having an important role in KCN degradation in the K. oxytoca, we constructed cyd- mutant to explore the possible role in KCN degradation. In this study the sequence of the genes encoding this terminal oxidase (cydAB) of K. oxytoca mutant were deduced. Results showed that cytochrome d oxidase of K. oxytoca is not a cyanide-insensitive oxidase, but playing an important role in KCN degradation.