OBJECTIVE：To investigate the effects of Periplaneta americana extract on the proliferation and apoptosis of human non-small cell lung cancer A 549 cells as well as its possible mechanism. METHODS ：The dry bodies of P. americana were soaked with 90％ ethanol and eluted with gradient water-methanol by polyamide column chromatography. The 20％，30％，40％， 50％，60％，70％，80％，90％ methanol elution sites （YS-A-H）were obtained. MTT method was used to screen the active site ， and the inhibition rate of different doses of active site was detected. Flow cytometry was adopted to detect cell apoptosis ，cell cycle and mitochondrial membrane potential of cells after treated with different doses of active site. RESULTS ：Half inhibition concentrations of YS-A-H were （95.25±8.42），（129.93±7.24），（221.28±12.68），（275.39±14.87），（276.76±16.32），（31.90± 5.34），（163.15±6.97），（122.81±8.36）μg/mL，respectively. YS-F had the strongest activity. After treated with 3，9，27，81 μg/mL YS-F for 24，48，72 h，cell proliferation inhibitory rate was increased significantly at different time points ；after treated for 48，72 h，that was significantly higher than same group after treated for 24 h；after 72 h treatment ，that was significantly higher than same group after 48 h treatment （P＜0.01）. There was no significant effect of 24 h treatment of 3 μg/mL YS-F and 72 h treatment of 9 μg/mL YS-F on the percentage of cells in the late stage of necrosis，24 h treatment of 3 μg/mL YS-F on the percentage of cells in G2/M phase and 48 h treatment of 3 μg/mL YS-F on the reduction rate of mitochondrial membrane potential（P＞0.05）. The percentage of cells in the early stage of apoptosis ，the late stage of apoptosis and the early stage of necrosis ，the late stage of necrosis，as well as the percentage of cells in the Sub-G 0/G1 and S phase at each time point were significantly increased in other different doses groups ，while the percentage of cells in G 0/G1 and G 2/M phase was decreased significantly （P＜0.01）. In each dose group，the percentage of cells in the early stage of apoptosis ，the late stage of apoptosis and the early stage of necrosis ，the late stage of necrosis （except for the percentage of cells in the late stage of necrosis treated with YS-F 9 μg/mL for 72 h）and the percentage of cells in Sub-G 0/G1 phase，G2/M phase （except for YS-F 27，81 μg/mL for 48 h）after treated for 48，72 h were significantly higher than same group after 24 h of treatment ；the percentage of cells in G 0/G1 phase，S phase and G 2/M phase （except for YS-F 9 μg/mL for 48 h）after treated for 48，72 h were significantly lower than same group after 24 h of treatment （P＜0.01）；the percentage of cells in the early stage of apoptosis ，the late stage of apoptosis and the early stage of necrosis ，the late stage of necrosis （except for the percentage of cells in the late stage of apoptosis and early stage of necrosis when treated with YS-F 27 μg/mL for 72 h，the percentage of cells in the late stage of necrosis when treated with YS-F 3，9 μg/mL for 72 h were decreased significantly ）and the percentage of cells in S phase （except for YS-F 3 μg/mL for 72 h）and Sub-G 0/G1 phase after treated for 72 h were significantly higher than same group after 48 h of treatment ，while the percentage of cells in G 0/G1 and G 2/M phase were significantly lower than same group after 48 h of treatment （P＜0.01）. After treated with YS-F 9，27，81 μg/mL for 48 h，the reduction rate of cell mitochondrial membrane potential was increased significantly ；YS-F 27，81 μg/mL groups were significantly higher than YS-F 9 μg/mL group，and YS-F 81 μg/mL group was significantly higher than YS-F 27 μg/mL group. CONCLUSIONS：YS-F can inhibit the proliferation and promote the apoptosis of A 549 cells by preventing cell transformation from S phase to G 2/M phase ，and reducing mitochondrial membrane potential ，in time-dependent or dose-dependent manner.