PROBLEM TO BE SOLVED: To provide a safe glucosyltransferase inhibitor which can be used for suppression of formation of dental plaque, prevention and treatment, etc., for periodontal diseases by formulating the inhibitor with compositions for oral cavity, foods and feeds, etc. SOLUTION: This glucosyltransferase inhibitor comprises solvent extracts of at least one or more kinds of plants selected from a group consisting of Cinnamomum sintok Bl. (Sintok), Eugenia polyantha Wight (Babakan salam), Cinnamomum burmani Nees ex Bl. (Kayu manis), Eugenia cuminii Merr. (Babakan duwet), Anacardium occidentale L. (Daun jambu mete), Peltophorum pterocarpum (DC.) Bakh (Kayu timur), Mesua ferrea (Sari kurung), Cinnamomum cassia Nees ex Bl. (Bunga lawang), Gendarussa vulgaris Nees (Gondoroso), Gymnopetalum leucosticum Miq. (Duri kemarung), wherein the above plant names in parentheses are represented by Indonesian names, and Phylanthus niruri Paraparami (Peru name : Chanca piedra).
