The aim of this study was to evaluate the effect of farnesol on the production of acids and hydrolytic enzymes by biofilms of and. The present study also evaluated the time-kill curve and the effect of farnesol on matrix composition and structure of single-species and dual-species biofilms. Farnesol, at subinhibitory concentrations, showed a significant reduction in biofilm acid production, but did not alter hydrolytic enzyme production. The number of cultivable cells of both microorganisms was significantly reduced after 8 h of contact with farnesol. Extracellular matrix protein content was reduced for biofilms formed in the presence of farnesol. In addition, confocal laser scanning and scanning electron microscopy displayed structural alterations in all biofilms treated with farnesol, which included reduction in viable cells and extracellular matrix. In conclusion, farnesol showed favorable properties controlling some virulence factors of and biofilms. These findings should stimulate further studies using this quorum-sensing molecule, combined with other drugs, to prevent or treat biofilm-associated oral diseases.