A Bacillus, ASSC-2, belonging to alkalophilic bacterium is known to grow at pH range of 6.5 to 10.5 (Oshima et al., 1987). The growth rate at neutral pH range was accelerated by addition of KCI to the growth medium. On the contrary, the growth rate at alkaline pH range was accelerated by addition of NaCl. Similar stimulative effect of salt to each pH also was observed in NADH oxidase. Incorporation of leucine into whole cells fractions was equally accelerated at pH 7 and 9. Higher concentration of K+ is absolutely required in growth of the bacteria at neutral pH, but not alkaline pH, compared with other conventional neutrophilic bacteria. Effects of potassium ions to growth of alkalophilic bacteria were discussed.