By mean of the glass electrode, the author investigated the buffer capacity of nutrient broth and peptone water, that were generally using in bacterial culture, and also studied the effects off buffer substance that gave rise of the buffer capacity when it was added to the media. Moreover, using the media obtained above, the author conduted the investigation of some change in the media by the preparation procedurs and of bacterial growth in it. The following results were obtained. 1) The buffer capacities of nutrient broth and peptone water were seemed to be depended upon the over-all action of substances contained in the media. However, the buffer capacity of each media could be depicted by entirely different curve at about pH 7.0; the curve for nutrient broth showed single peak at pH 7.0, while that for peptone water showed at pH 7.0 and rises either sides of this caving. 2) By the addition of phosphate buffer to peptone water, the peak was appeared around pH 7.0 on the buffer capacity cuve. The capacity curve obtained in this was resembled that obtained in composition from that of peptone water and phosphate buffer solution. 3) The pH deviation by sterilization was noticed in greater extent in nutrient broth than in peptone water, and less deviation of pH was observed in the media of which pH was adjusted by NaOH in comparison with the same media adjusted by Na(2)CO(3). There was no longer deviation of pH by the addition of phosphate buffer to the media in the concentration about M/100. 4) On any culture of E. coli communis, A. aerogenes and Sal. 57 S in peptone water to that phosphate buffer was added, the less deviation of pH of the media and much bacterial growth were observed compaired with the control. These evidences were also noticed more clearly on the culture of same organisms that were grown in the glucose added media. 5) The pH of the glucose added peptone water was decreased by the culture of E. coli communis or Sal. 57 S in the media and this condition turned out eventual standatill of the growth. However, by the adjustment of pH of the media to the same range as before, it was observed the growth of the organism recovered well in comparison with the control.