The main purpose of this study was to investigate the active components of the Chinese medicine formula Shenqi San (SS) by high performance liquid chromatography with diode array detector and electrospray ionization-hybrid quadrupole time-of-flight mass spectrum (HPLC-DAD-ESI-QTOF-MS),and demonstrate the anticancer mechanism of SS on human lung adenocarcinoma A549 cells by evaluating the cell proliferation and apoptosis induction.The chloroform extraction of SS (CE-SS) was extracted from SS,while HPLC-DAD-ESI-QTOF-MS assay was performed to identify components of CE-SS.MTT assay was used to quantify the proliferation of A549 cells with the treatment of CE-SS.Apoptosis analysis was carried out by detecting phosphatidylserine (PS) extalization using the Annexin V-FITC Apoptosis Detection Kit and the stained cells were analyzed with a flow cytometer.DAPI staining assay was carried out to observe morphological characteristics of apoptotic cells.West blotting was used to detect the expression of important signaling proteins including caspase-3,-8,-9,p53,Bax and Bcl-2.Eight compounds were identified through HPLC-DAD-ESI-QTOF-MS analysis and 3-pyridine carboxylic acid,barbatin C,scutebarbatine F and barbatine D might be the main compounds responsible for the antitumor effect of CE-SS.CE-SS suppressed the proliferation of lung cancer A549 cells in a time-and dose-dependent manner.By Annexin V-FITC/PI double staining,we found that treatment with CE-SS induced apoptosis in A549 cells.After 24-h exposure to CE-SS,the expression of cleaved-caspase-9,cleaved-caspase-8 and cleaved-caspase-3 protein was activated,the expression of p53 protein increased while the ratio of Bax/Bcl-2 also increased.This study identified the eight compounds of CE-SS,and demonstrated their anticancer effect on human lung adenocarcinoma A549 cells via induction of apoptosis.