[PROBLEMS] To provide a novel therapeutic agent for a periodontal disease which is excellent in the effect of preventing abnormal extension of a gingival epithelial tissue. [MEANS FOR SOLVING PROBLEMS] A therapeutic agent for a periodontal disease comprising a separated ingredient produced by extracting a raw material plant belonging to the family Salicaceae, the genus Salix with a solvent； and a composition for oral application which can be used for treatment of an oral disease such as gingivitis and periodontitis.
