The aim of this study was to examine the effects of 7-epiclusianone, a new prenylated benzophenone isolated from the plant Rheedia gardneriana, on some of the virulence properties of Streptococcus mutans associated with biofilm development and acidogenicity. The synthesis of glucans by glucosyltransferases B (GTF B) and C (GTF C) was markedly reduced by 7-epiclusianone showing more than 80% inhibition of enzymatic activity at a concentration of 100 μg mL−1. Double-reciprocal analysis (Lineweaver–Burk plots) revealed that the inhibition of GTF B activity was noncompetitive (mixed) while GTF C was inhibited uncompetitively. The glycolytic pH drop by S. mutans cells was also disrupted by 7-epiclusianone without affecting the bacterial viability, an effect that can be attributed, in part, to inhibition of F-ATPase activity (61.1±3.0% inhibition at 100 μg mL−1). Furthermore, topical applications (1-min exposure, twice daily) of 7-epiclusianone (at 250 μg mL−1) disrupted biofilm formation and physiology. The biomass (dry-weight), extracellular insoluble polysaccharide concentration and acidogenicity of the biofilms were significantly reduced by the test agent (P<0.05). The data show that 7-epiclusianone disrupts the extracellular and intracellular sugar metabolism of S. mutans, and holds promise as a novel, naturally occurring compound to prevent biofilm-related oral diseases.