OBJECTIVE:To evaluate the anti-tumor activity of ethyl acetate fraction (EFA),extracted with ethanol from the root of Dai-Bai-Jie in A549 cancer cells and its underlying mechanism.METHODS:Dai-Bai-Jie was extracted with 95％ ethanol-aqueous (DBJ-1),50％ ethanol-aqueous (DBJ-2),and water (DBJ-3) by reflux method.95％ ethanol-aqueous extract was separated byethyl acetate (EFA) and n-butyl alcohol (DBJ-5),consecutively.The SRB method was used to evaluate the cytotoxic activity.Annexin V-FITC staining was applied to observe the apoptosis and analyze the cell cycle activated by EFA in A549 tumor cell.West blot was used to detect the apoptosis/related proteins expressions.A549 tumor cellsbearing nude mice model was employed to measure the tumor volume,mice weight,and tumor inhibition ratio in order to verify the antitumor activity in vivo.RESULTS:DBJ-1 and EFA showed better cytotoxic activity on A549 tumor cells with IC50 25 and 3.5 μg/ mL,respectively.EFA can exhibit the proliferation,arrest cell cycle at G0/G1 phase,and induce apoptosis in A549 tumor cells in vitro.The mechanisms of apoptosis induced by EFA may be associated with decreasing Bcl-2 protein expression and increasing p53,Bax,Caspase-3,and Caspase-8 proteins expression.EFA also possessed significant anti-tumor efficacy in nude mice,and little toxicity was observed in the host.CONCLUSION:EAF could induce A549 tumor cells apoptosis and G0/G1 cell cycle arrest.A549 tumor cells apoptosis induced by EAF may be associated with the decrease in the ratio of Bcl-2 and Bax mRNA levels,and increase in the expression of p53,Caspase-3,and Caspase-8 proteins.