Abstract: Objective: To study the effect of β-elemene combined wi th radiotherapy on the expression of KU70mRNA and apoptosis of lung adenocarcinoma cell line A 549 . Methods:A549 cells were divided into the control group (c), irridation group (IR), β-elemene group (0.1 × IC 50and 0.2 × IC 50i.e. 10μ g/mL and 20μ g/mL β-elemene ) and β-elemene combined with irridation group (0.1 × IC 50+ IR and 0.2 × IC 50+ IR). IC 50was obtained through MTT method and cell survival rate was analyzed by colony formation test. Cell cycle and apoptosis were detected with flow cytometry. The expression level of KU70mRNA was detected by RT-PCR.Results: MTT assay showed that IC50value of A 549 cells was 120 μ g/mL. The number of cel l clones and survival rate of β-elemene groups were decl ined signi ficantly. The radiosensi tivi ty of A549 cells can be enhanced by β-elemene. The flow cytometry confi rmed that the ratio of G2/M and apoptosis were significantly in-creased under the effect of β-elemene, statistical ly di fferent from those in the control group (P <0.05). The expression level of KU70 mRNA in β-elemene wi th radiotherapy group was decl ined signi ficantly, statistical ly di fferent from those in the con-trol group (P <0.05). Conclusion:The radiosensi tization effect of β-elemene on A549 cells is associated with induction of cell apoptosis and down-regulation of KU70mRNA expression.