Following results were obtained with yeasts cultivated in malt-juice. (1) By examining the multiplication of yeasts by use of micetocrite method, and their fermentation action by Lane's method, it is stated that both processes are prohibited by high pressure, but after release from the compression they become equal to the control gradually, (2) Morphological changes of yeasts are not observed. (3) The vitality of yeasts is not influenced by hydrostatic pressure up to 1600 kg/c㎡.