Dental caries has been reported to be infectious disease by Streptococcus mutans(S. mutans). The ability of S. mutans to produce dental plaque has been shown to be related to glucan synthesis from sucrose by glucosyltransferase (GTase). Glucan is known to play an important role in the initiation of smooth surface caries. For preventing dental caries by traditional medicines, two hundred kinds of natural products were assayed for inhibiting activity against S. mutans and GTase. During the assay course, we chose some active plants against S. mutans and GTase and then applied these plant extracts to toothpaste.