Abstract: OBJECTIVE To study the chemical components of Fructus Xanthii's water-soluble ingredients. METHODS The finger-prints of Fructus Xanthii's water-soluble ingredients were established and the chemical components were identified by the method of LC-MS/MS. RESULTS Fructus Xanthii's five kinds of phenolic acids'chemical belonging were identified， and the structures were speculated. They are caffeoylquinic acid and dicaffeoylqcinic acid. CONCLUSION The identification of the chemical components of Fructus Xanthii can significantly enhance the accuracy and specificity of quality control. The qualitative and quantitative study of its chemical components can effectively control the quality of Fructus Xanthii and the relevant products.