Abstract: Objective To explore the inhibitory effect of formononetin （Form） on proliferation and epithelial mesenchymal transition （EMT） of non-small cell lung cancer A549 cells. Methods The A549 cells were cultured with Form （a final concentration of 0.1， 1， 10， 100 μmol／L）. The cell proliferation was determined at 24， 48， 72 and 96 h posttreatment by MTT method in control group and From group. The Annexin V-FITC／PI double staining combined with flow cytometry and quantitative realtimepolymerase chain reaction were applied to measure the early-apoptotic and late-apoptotic rates and expression of apoptosis related genes at 48 h after treatment. Western blotting was used to detect the EMT related molecular markers， including E-cadherin， N-cadherin and Vimentin. The supernatant levels of fibronectin （FN） were measured at 24， 48， 72 and 96 h by enzyme linked immunosorbent assay. Results Form exerted the inhibitory effect on the proliferation of A549 cells in the range of 1-100 mol／L， and presented in a dose- and time-dependent manner. In addition to 0.1 mol／L at 24-48 h， the proliferation inhibiting rates of Form were higher than those of control group （P＜0.05）. Compared with the control group， there were higher levels of early-apoptotic and late-apoptotic rates and mRNA levels of Bax and Bak but lower Bcl-2 mRNA levels in Form groups with statistical significance （P＜0.05）. In response to Form， there were increased E-cadherin but decreased N-cadherin， Vimentin and FN in comparison with control group at 48 h. Conclusion Form has a toxic effect on A549， which not only inhibit the proliferation and induce apoptosis. It may be related to the inhibition of the EMT process.