The problems to be solved by the invention are to provide antibacterial agents originated from natural products that are safe for regular use with potent antibacterial activity, and antibacterial compositions containing said antibacterial agents. Antibacterial agents containing Eysenhardtia adenostylis extract or isoflavan compounds are a solution to the problem. Also antibacterial agents containing Eysenhardtia adenostylis extract or isoflavan compounds as active ingredients. The antibacterial agents can be applied to products such as cosmetics, including quasi-drugs, pharmaceuticals and foods. Further, antibacterial compositions containing these antibacterial agents, Eysenhardtia adenostylis extract or isoflavan compounds, and other compositions such as cosmetics, including quasi-drugs, pharmaceuticals and foods.