Survival of thermotolerant Lactobacillus reuteri KUB-AC5 in 20% (w/v) skim milk was found to be 11.3% after spray drying by using a pilot scale spray dryer with inlet temperature at 170°C and outlet temperature at 85°C. The ability of dried cell to produce antimicrobial activity was not affected by the spray drying. The model system for predicting viability of spray-dried L. reuteri KUB-AC5 during long-term storage was established, based on the Arrhenius equation, and verified by experimental data, because the viability of cells during storage can be correlated with storage temperature. The viability during storage at 30oC declined more rapidly than that storage at 4°C.