Abstract: To provide an antibacterial agent effective against gram-positive bacteria, particularly an antibacterial agent that is safe even when added to foods and the like, and a disinfecting method. An antibacterial agent comprising as an active ingredient either one or both of compounds represented by the following formula (1) and (2) contained in a labiatae plant extract: This antibacterial agent has antibacterial activity against gram-positive bacteria belonging to the genus Staphylococcus, the genus Lactobacillus, the genus Listeria, the genus Alicyclobacillus or the genus Bacillus.