【Background】 Being capable of strongly exerting allelopathic effects on neighboring plants possibly would be the most important factors that enables Eupatorium adenophorum to be such a strongly aggressive plant worldwide. Presently, studies on potential allelochemicals of E.adenophorum were mainly focused on less polar compounds, especially terpenoids, while few reports is focusing on large polar ones. 【Method】 Bioassaydirected phytochemical study was carried out to isolate potential allelochemicals from polar subfractions of EtOAc extract of E.adenophorum. The chemical structures of the purified compounds were identified by spectroscopy, including MS and NMR techniques. The allelopathic potential of subfractions of EtOAc extract and isolated pure compounds as well as two literature reported terpenoid allelochemicals, 8hydroxy4cadinen3one (2) and 4,7(11)cadinadiene3,8dione (3), and signaling compound JAIle, were all evaluated by detecting their inhibitory activity against seeds germination and seedling root growth using Arabidopsis thaliana as test plant. 【Result】 A bioactive compound was isolated from one polar subfraction of EtOAc extract of E.adenophorum and its chemical structure was identified as 2coumaric acid glucoside (1). Bioassay indicated that compound 1 showed significant inhibitory activity against A.thaliana seedling root growth at concentration as low as 0.[KG-*8]1 mmol〖KG-*2〗·〖KG-*4〗L-1, which is more potent than the other two identified compounds. A closely similar inhibition pattern of 1 to that of the signaling compound JAIle were also observed. 【Conclusion and significance】In addition to less polar terpenoids, potentially existing large polar allelochemicals in E.adenophorum might significantly contribute the total allelopathic effects. The discovery of compound 1 and other potential polar allelochemicals from E.adenophorum may significantly promote the elucidation of the potential allelopathic mechanism possessed by this wellknown invasive plant.