Bakuchiol was isolated from the seeds of Psoralea corylifolia, a tree native to China with various uses in traditional medicine, followed by extraction with ether and column chromatography combined with silica gel and octyldecyl silane. In this study, the antimicrobial activities of bakuchiol against some oral microorganisms were evaluated in vitro. The cell growth of Streptococcus mutans was inhibited in a bakuchiol concentration-dependent manner, and growth of S. mutans was completely prevented by 20 µg of bakuchiol per ml. The bactericidal effect of bakuchiol on S. mutans was dependent on temperature and stable under the following conditions: sucrose, 0 to 10% (wt/vol); pH, 3.0 to 7.0; organic acids (3% [wt/vol] citric and malic acids). Bakuchiol showed bactericidal effects against all bacteria tested, including S. mutans, Streptococcus sanguis, Streptococcus salivarius, Streptococcus sobrinus, Enterococcus faecalis, Enterococcus faecium, Lactobacillus acidophilus, Lactobacillus casei, Lactobacillus plantarum, Actinomyces viscosus, and Porphyromonas gingivalis, with MICs ranging from 1 to 4 µg/ml and the sterilizing concentration for 15 min ranging from 5 to 20 µg/ml. Furthermore, bakuchiol was also effective against adherent cells of S. mutans in water-insoluble glucan in the presence of sucrose and inhibited the reduction of pH in the broth. Thus, bakuchiol would be a useful compound for development of antibacterial agents against oral pathogens and has great potential for use in food additives and mouthwash for preventing and treating dental caries.