In this study, the combined effects of lipid-soluble nhexane extract of red ginseng marc (HERGM) and water-soluble L-arginine, which has been reported to have anticaries activities, on biofilm formation and glucosyltransferase (Gtase) activity of S. mutans were investigated by checkerboard assay method. The combination of HERGM and L-arginine showed additive effects on both inhibition of biofilm formation and GTase activity of S. mutans with a fractional inhibitory concentration index of 0.75, respectively. When HERGM and L-arginine were treated together, the inhibition of biofilm formation was mainly attributed to Larginine, and the inhibition of GTase activity was attributed to HERGM. These results indicate that L-arginine and HERGM complementarily inhibits the biofilm formation of S. mutans.Keywords L-arginine · Biofilm inhibition · Glucosyltransferase · n-hexane extract of red ginseng marc · Streptococcus mutans 서 론