Each oxidoreductase activity of the aerobic respiratory chain-linked NADH oxidase system in the marine bacterium Pseudomonas nautica was stimulated by monovalent cations including $Na^+,;Li^+,;and;K^+$. In the presence of NADH or deamino-NADH as electron donors, $GH_2$ formation was approximately 1.3-fold higher in the presense of 0.08 M of $Na^+;than;K^+$, Whereas the other reductase activities were not significantly higher in $Na^+;than;K^+$. The optimal pH of NADH (or deamino-NADH):ubiquinone-1 oxidoreductase was 9.0 in the presence of 0.08 M NaCl. The activity of NADH (or deamino-NADH):ubiquinone-1 oxidoreductase was inhibited by about 33% with $60{mu}M$ 2-heptyl-4-hydroxyquinoline-N-oxide (HQNO). The activity of NADH (deamino-NADH): ubiquinone-1 oxidoreductase was inhibited by about 32 to 38% with $80{mu}M$ rotenone, whereas the activity was highly resistant to capsaicin. On the other hand, electron transfer from NADH or deamino-NADH to ubiquinone-1 generated a membrane potential (${Delta}{psi}$) which was larger in the presence of $Na^+$ than that observed in the absence of $Na^+$. The ${Delta}{psi}$ was almost completely collapsed by $5{mu}M$ carbonylcyanide m-chlorophenylhydrazone(CCCP), and approximately 50% inhibited by $100{mu}M$ rotenone, or $60{mu}M$ 2-heptyl-4-hydroxyquinoline (HQNO). Also, HQNO made the ${Delta}{psi}$ very unstable. The results suggest that the enzymatic and energetic properties of the NADH:ubiquinone oxidoreductase of P. nautica are quite different, compared with those of other marine halophilic bacteria.