Backgrounds/Aims: To clarify the usefulness of Lactobacillus casei strain Shirota (LcS)-fermented milk in the normalization of bowel movements and improvement of infection control for the elderly residents and staff of facilities for the elderly. Methods: A randomized placebo-controlled double-blind test was performed among the elderly residents (average age, 85) and staff members (average age, 37) of facilities for the elderly. The participants randomly received either LcS-fermented milk or a placebo beverage once daily for 6 months. Clinical data and enteric conditions were compared between the 2 groups. Results: A significantly lower incidence of fever and improved bowel movements were seen in the LcS-fermented milk group (n = 36) in comparison to the placebo group (n = 36). The numbers of Bifidobacterium and Lactobacillus were significantly higher (p < 0.01), the numbers of destructive bacteria such as Clostridium difficile were significantly lower (p < 0.05), and the fecal acetic acid concentration and total acidity were significantly higher in the LcS group. A significant difference in the intestinal microbiota, fecal acetic acid, and pH was also observed between the LcS and placebo groups among the facility's staff members. Conclusions: The long-term consumption of LcS-fermented milk may be useful for decreasing the daily risk of infection and improving the quality of life among the residents and staff of facilities for the elderly.