A novel, speedy and reliable LC-MS-MS method for the search, identification and quantitation of O-glycosides and their aglycones from plant resources was established by analyzing the extract of Erigeron breviscapus. The extract was directly infused to a triple-quadrupole MS-MS and major glucuronides in the extract were screened out with high confidence by a neutral loss scan for the loss of a gluconic acid. The identity of these glucuronides and their aglycones was further confirmed with LC-MS-MS. In addition to scutellarin, apigenin 7-O-glucuronide, quercetin-3-O-glucuronide and their aglycones that were previously reported by others, we also confirmed by LC-MS-MS that remarkable amount of baicalin, an isomer of apigenin 7-O-glucuronide, presented in the extract of this plant, which had not been reported before. A satisfying quantitation of three glucuronides was also made by LC-MS-MS.