Lactobacillus crispatus KT-11, which was originally isolated from the feces of healthy infants, has been reported to show multiple immunoregulatory effects. However, there have been no reports about the effect of the Lactobacillus on periodontal disease, a chronic destructive inflammatory disease of the tissues supporting the teeth. We used a model of periodontal disease in which mice were infected with Porphyromonas gingivalis. As we report here, oral ingestion of KT-11 exerted inhibitory effects on alveolar bone resorption in this model, suggesting potential preventive activity of the Lactobacillus in periodontal disease.Mice were given free access to feed containing dead Lb. crispatus KT-11 over 6 weeks, and were then orally infected with P. gingivalis 10 times for 2 weeks from 4 weeks later ofLb. crispatus KT-11 administration. The results showed a marked attenuation of alveolar bone resorption in mice that ingested the Lb. crispatus KT-11-containing feed. Induction of total IgG in plasma and total secretory IgA in saliva was observed. A specific plasma IgG antibody response to P. gingivalis also was induced.Based on the immune response to P. gingivalis infection induced by ingestion of Lb.crispatus KT-11, this study suggests that oral administration of Lb. crispatus KT-11 is effective in preventing chronic periodontitis.