In the previous study, we have isolated several vaginal lactobacilli from Korean woman and selected one of them (KLB12) for further study, which was indentified as Lactobacillus fermentum by sequence analysis of 16S rRNA gene. Formulated L. fermentum KLB12 can be used for ecological treatment of bacterial vaginosis. For pharmaceutical formulation, the spray-drying process is required where stress such as high temperature is routinely applied. In this study, we found that heat stress at 60$^{circ}C$ for 20∼30min reduced the viable cell population of KLB12 by 10$sub$6/～10$sub$9/. However, adaptation of KLB12 cells at 52$^{circ}C$ made them more thermotolerant upon exposure to 60$^{circ}C$. The level of thermal protection in RSM (reconstituted skim milk) by adaptation in acid (pH 5), cold (4$^{circ}C$), ethanol (3％), NaCI (0.3M) was also examined. Although not as efficient as the homologous stress, adaptations in both cold and NaCI gave considerable cross protection against heat stress. When chloramphenicol was added during heat adaptation, adaptation effect was abolished. This suggests that de novo protein synthesis is necessary during the adaptation process. Important changes in proteome during heat adaptation was examined with two-dimensional gel electrophoresis.