PROBLEM TO BE SOLVED: To provide a novel plant-derived antibacterial agent having high safety, easily available raw materials, and excellent antibacterial activity. Provision of an effective antibacterial method using the antibacterial agent. An antibacterial agent containing a chestnut bark extract as an active ingredient. Cosmetics containing the antibacterial agent. The chestnut bark extract has antibacterial activity against Staphylococcus aureus and is obtained by extracting chestnut bark in an extraction solvent containing at least one selected from the group consisting of water and a hydrophilic solvent. [Selection diagram] None【課題】安全性が高く、原料が容易に入手可能であり、優れた抗菌活性を有する、植物由来の新規な抗菌剤の提供。前記抗菌剤を用いた効果的な抗菌方法の提供。【解決手段】栗皮抽出物を有効成分として含む抗菌剤。前記抗菌剤を含む化粧料。前記栗皮抽出物は、黄色ブドウ球菌に対する抗菌活性を有し、栗皮を、水及び親水性溶媒からなる群から選ばれる少なくとも１種を含む抽出溶媒中にて抽出して得られる。【選択図】なし
