We proposed new counting method of the number of active bacterium by using micro-droplet as an incubator (figure 1).During the cultivation,the change of bacteriums behavior or the change of chemical and physical property might be enhanced due to its small droplet volume.Therefore,by counting the number of droplet which indicates these changes,it might be possible to estimate the number of active bacteria rapidly.We fabricated a micro-channel chip to generate and store micro-droplets (figure 2),each of which contains single bacterium at most.In the experiment E.coli (strain Escherichia coli K-12) was used as bacteria.In order to formation micro-droplets,flow rate of sample which E.coli suspended in LB medium was 1 μL/min and flow rate of Fluorinert was 10 μL/min (figure 3).After formation micro-droplets,two inlets and outlet were blocked,and micro-channel chip was put into constant temperature water circulation equipment which we made newly to maintain cultivation temperature (figure 4).First,we examined several micro-droplets which has one E.coli by using microscope,and then we took pictures of microscopic video image of those micro-droplets at intervals of 30 minutes for 6 hours.We checked whether the E.coli could be cultivated in such a small volume of micro-droplet.Figure 5 shows experiment setup.In this experiment,the water temperature of the constant temperature water circulation equipment was set to be 28 ℃,37 ℃ and 40 ℃.We measured cultivation speed of E.coli in micro-droplets.Figure 6 shows,the image of micro-droplet when the water temperature was 37℃.Numerous E.coli were observed in a micro-droplet in 6 hours.As shown in figure 7,cultivation speed in the water temperature of 37℃ was larger than those in other conditions (figure 7).Moreover,active E.coli that was increased in micro-droplet and inactive E.coli that was not increased in micro-droplet was counted in the three conditions (table 1).This result indicates,it may be possible to estimate the number of initially active E.coli by this method.