Streptococcus mutans (S. mutans) plays an important role in the information of dental plaque and it is being noticed as major causative bacteria of dental caries. In the present study, inhibitory effects of the ethanol extract of Dianthus superbus Linne (D. superbus) on the growth, acid production, adhesion and water-insoluble glucan synthesis of S. mutans were examined. The ethanol extract of D. superbus (0.5 - 4 mg/ml) significantly lowered the growth of S. mutans in a dose dependent manner. The acid production of S. mutans were inhibited by the presence of ethanol extract of D. superbus(1 - 4 mg/ml) significantly. The ethanol extract of D. superbus (0.25 - 4 mg/ml) also significantly lowered the adherence of S. mutans in a dose dependent manner. In water-insoluble glucan synthesis assay, 0.25 - 4 mg/ml of the ethanol extract of D. superbus significantly inhibited the formation of water-insoluble glucan. These results suggest that D. superbus may inhibit the caries-inducing properties of S. mutans. Further studies are necessary to clarify the active constituents of D. superbus responsible for such biomolecular activities.