To explain the relation between the effect of disinfectants on the respiration of bacteria and the bactericidal action, the author observed the effects of disinfectants on the respiration of E. coli and Staph. aureus by means of conventional warburg's manometer, and the bactericidal effect to these bacteria by subcultering the surviving cells in the cup content of wardurg's manometer after the studies on the respiration described above. Moreover, the bactericidal effect was studied from the viewpoint of action time of disinfectants. The following results were obtained. 1) As for the relation between the effect on respiration and the bactericidal action, a marked inhibition on the respiration of bacteria was observed by commonly used disinfectant in such dilution as it could render bactericidal effect. Both the bactericidal effect and the inhibition on respiration were more severe at the disinfectant that had the effect even in higher dilutions. 2) On the test using aureomycin, it did not render bactericidal effect at all at the concentration that the respiration was inhibited almost completely. Hence aureomycin should have worked bacteriostatically. 3) In the case of macramin a severe inhibition on the respiration was found in a fairly high dilution. However, the bactericidal effect could not observe at the minimal dilution that could inhibit the respiration almost completely, and only slight innibition of growth of bacteria was found at that dilution. 4) The relative bactericidal effect of disinfectants found to be comparable each other by means of the minimal action time requied to kill the organism in the minimal concentration that rendered the inhibition on respiration of the bacteria.