The time repuired for killing bacteria varies with the effcetive concentration of the disinfectants which give a bactericidal effect on bacteria. The author investigated the enzyme activity of the bacterial cells obtained at various lenghth of the time of disinfection by observing the respiration of that cells. And the following results were obtained. 1) The respirations were measured on the bacterial cells which were lost growth capacity by the action of disinfectants in various concentration. There were not found acceleration of the respiration at the expense of many substrates except lactate, at with the acceleration of the respiration was found to some extents. 2) From the viewpoint of the respiration, the inhibition on the enzyme activity of bacteria differed from the disinfectants. Namely, the disinfectant which showed strong bactericidal effect inhibited the respiration markedly, but the disinfectant whose action was mild did not show such maked inhibition. 3) As mentioned above, the time required for killing bacteria varies with the actual concentration of disinfectant. But the inhibition on the enzyme activity of bacteria occured more severly on the bacterial cells killed by a prolonged action of dilute disinfectant than on the cells killed by shor-time action of the disinfectant having high concentration.