Streptococcus mutans (S. mutans) forms part of the commensal microflora and is deemed to be the major pathogen responsible for the generation of dental caries. The enzyme, sortase A enzyme, modulates the surface properties and cariogenicity of S. mutans. Curcumin has been reported to be an inhibitor of Staphylococcus aureus sortase A. In this study, inhibition of a purified S. mutans UA159 sortase A by curcumin was evaluated. Curcumin exerted strong inhibitory activity with a half maximal inhibitory concentration (IC50) of 10.2 +/- 0.7 mu M which was lower than the minimum inhibitory concentration of 175 mu M and the minimum bactericidal concentration of 350 mu M. These results indicated that curcumin is a S. mutans UA159 sortase A inhibitor and therefore represents as a promising anticaries agent.