We investigated the improvement in intestinal function and the constipation preventive and remedial effects of the fermented milk product R&B Rhythm(R) in mice and rats. The results showed that the effects varied significantly among different doses. The digestive tract transfer rate increased dramatically in a dose-dependent manner in both animals. Compared with treating constipation with loperamide alone, treatment with loperamide and the fermented milk R&B Rhythm improved the number of fecal pellets from the animals, suggesting that it is effective for preventing and relieving constipation. Both the quantity of feces and water content of the feces increased significantly at high levels of yogurt feeding. These results suggest that repetitively ingesting fermented milk products could be effective for preventing and treating constipation symptoms.