Effects of ethanol on the cell wall and the cytoplasm of true hiochi-bacilli ( Lactobacillus heterohiochii H 1, L. homohiochii S 33), hiochi-lactobacilli (Hetero fermenter H 34, Homo fermenter R 13), and general lactic acid bacteria ( L. brevis NRIC 1031, L. sake NRIC 1070) were investigated, and following results were obtained. 1) The thickness of cell walls of each true hiochi- bacilli cultivated with 0 or 7% ethanol was the same. However, the cell walls of each hiochilactobacilli and each general lactic acid bacteria cultivated in the media containing 7% ethanol was thicker than those of cells cultivated without ethanol. In the media of high concentration of ethanol, compared with the medium containing no ethanol. The cell wall of L. heterohiochii H 1, L. homohiochii S 33, hetero-fermentative hiochi-lactobacilli H 34, homo-fermentative hiochi-lactobacilli R 13, general lactic acid bacteria L. brevis and L. sake grown in the presence of high concentration (10, 15 or 17%) of ethanol was about 2, 1.6, 1.5, 1.3, 1.3 and 1.1 times as thick respectively as compared with that of cells grown without ethanol. The thickness of the cell wall was tended to be heavy in the order, general lactic acid bacteria, hiochilactobacilli and true hiochi-bacilli. From these results, it was suggested that the thickness of cell wall was related to the alcohol tolerance of true hiochi-bacilli. 2) The cytoplasm of each bacterium was not affected by ethanol.