To investigate the mechanism of action by which farnesol functions as an antibacterial agent and inhibits Staphylococcus aureus growth, the growth rates of S. aureus cultured in farnesol versus S. aureus cultured in farnesol and supplemented with 3-hydroxy-3-methylglutaryl (HMG)-CoA or mevalonate were compared. The investigation was designed to observe whether farnesol affected on the mevalonate pathway by using the intermediate metabolites of the pathway. The resulting growth curves demonstrated that mevalonate reduced the antibacterial activity of farnesol, but HMG-CoA did not inhibit farnesol. These results suggest that farnesol affects the mevalonate pathway. Moreover, farnesol inhibited HMG-CoA reductase activity in an in vitro enzymatic assay.