Salvia yunnanensis, S.przewalskii var. przewalskii, and S.castanea are three species of the Salvia plants in China. In order to discover the biologically active compounds, their free radical scavengers were screened based on an off-line and on-line HPLC-2,2′-azinobis-(3-ethylbenzothiazoline-6-sulfonate) (ABTS) assay coupled with a diode array detector and tandem mass spectrometry. In the off-line assay, the roots and rhizomes (the underground part) of S. przewalskii displayed the strongest antioxidant properties, while the leaves and stems (the aerial part) of S. yunnanensis displayed the weakest activities. In the on-line assay, all of the underground parts and the aerial parts of the three plants were tested by HPLC and the underground parts of S. yunnanensis and S. przewalskii, as well as the aerial part of S.przewalskii were analyzed by LC-ESI MSn. Among the seventeen antioxidants screened, tanshinone I, salvianolic acid B, and tanshinone IIA were confirmed by authentic standards; and another five compounds were tentatively identified based on the tandem mass spectroscopy. 7,20-Epoxyroyleanone, tanshinone I, and 1-oxoferruginol were reported as antioxidants for the first time. Using the on-line method, the order of antioxidant activities was found to be salvianolic acid B > vitamin C > tanshinone I > tanshinone IIA. Furthermore, it was observed that the regression curve between negative peak areas and sample concentrations could be inflected at high concentrations. © 2014 Copyright Taylor and Francis Group, LLC.