The authors studied the viability and pH of Lactobacillus casei which was isolated from the Yakult in terms of its storage temperature time(days). The following results have been obtained: (1) The viability test to Lactobacillus casei under storage in 4$circ$C temperature condition in 35 days, has shown that the original population of $4.0 imes 10^8$ organisms was decreased to $0.1 imes 10^8$, under storage in 10$circ$C temperature the organisms to $0.08 imes 10^8$, in room temperature the organisms to $0.009 imes 10^8$, and in 35$circ$C temperature the organisms to $0.0009 imes 10^8$. The correlation coefficient of storage period (days) and number of bacterial viability were significant as r=0.956(p<0.01) in 4$circ$C, r=-0.999 (p<0.01) in 100C, r=0.975(p<0.01) in room temperature and r=-0.923(p<0.01) in 35$circ$C. (2) The pH test to Lactobacillus casei unde.r storage in 4$circ$C temperature condition for 35 days has shown that the original pH of 3.54 were acidified to 3.35, under storage in 10$circ$C temperature the pH were acidified to 3.20, in room temperature the pH were acidified to 3.15, and in 35$circ$C temperature the pH were acidified to 3.0. The correlation coefficient of variation of pH between storage period (days) and temperature were significant as r=-0.972(p<0.01) in 4$circ$C, r=-0.922 (p<0.01) in 10$circ$C, r=-0.963 (p<0.01) in room temperature and r=-0.953 in 35$circ$C.