In this study we evaluated the effect of prenylated peanut stilbenoids on the growth, biofilm accumulation and acid production of the dental caries pathogen Streptococcus mutans. Prior research with the non-prenylated stilbenes, resveratrol and piceatannol, has shown that these molecules are active against S. mutans. Here we sought to determine if the addition of a prenyl group to the stilbene backbone increased anti-S. mutans activities. Two prenylated stilbenes, arachidin-1 and arachidin-3, were produced using a peanut hairy root production system. Compared to resveratrol and piceatannol, both arachidin-1 and arachidin-3 led to greater inhibition of S. mutans planktonic growth. This effect also led to reduced biofilm formation, by inhibiting growth, instead of a specific action against biofilm cells. Lastly, sub-MIC concentrations of arachidin-3 reduced the acid production of S. mutans above the ‘critical pH’ that leads to tooth enamel erosion. In summary, stilbenoids have anti-S. mutans activity, and prenylation enhances this activity.