Objective:To study the antitumor mechanism of W40,a monomer purified from Wedelia prostrate (Hook.et Arn.) Hemsl.Methods:The effects of W40 on the cell proliferative of GLC-82 cells were detected by MTT assay and colony formation assay.The migratory abilities of GLC-82 cells were observed by wound healing assay.Cell apoptosis was evaluated by Annexin V-FITC/PI staining analysis.The levels of apoptosis-relative proteins and cell proliferation-related proteins,such as Caspase-3,PARP,Stat3 and ERK,were detected by Western blotting.Results:MTF assay showed that W40 had a significant cytotoxic effect on non-small cell lung cancer GLC-82 cells.Colony formation assays showed that W40 significantly inhibited GLC-82 cells proliferation.The migration of GLC-82 cells was inhibited by W40 in a dose-dependent manner.Flow cytometry showed that the apoptotic rate increased gradually in a concentration-dependent manner.W40 down-regulated Stat3 as decreasing p-Stat3 and downstream proteins of Bcl-2 and Mcl-1.At the same time,W40 up-regulated the expression of pro-apoptotic protein Bax,and increased the cleavaged Caspase-9,Caspase-3 and PARP.W40 also down-regulated BRAF / MAPK / ERK signal pathway as decreasing p-BRAF,p-MEK and p-ERK.Conclusions:W40 induced apoptosis by inhibiting BRAF / MAPK / ERK and Stat3 signaling pathways.