Objective: To explore the effect and possible mechanism in vitro of radiosensitization by β-Elemene in A549 cell line from adenocarcinoma of lung. Methods: The A549 cell line from adenocarcinoma of lung was chosen for the study to determine the inhibition ratio by using MTT assay. Morphologic change, growth curve, cloning efficiency, divisional index were observed. Change of cell cycle and apoptosis rate were analyzed by FCM and the expressions of gene P53 and Bcl-2 were detected. Results: Reproductive activity of the group which was under irradiation and β-Elemene was significantly sup- pressed and its cloning efficiency and divisional index also declined. The apoptosis rate of the group which was under irradia- tion and β-Elemene was significantly higher at 48 h and 72 h, which was analyzed by FCM. The expression of P53 without Bcl-2 was observed in the group under irradiation and β-Elemene and the group under β-Elemene only at the 48th hour point, while the expression of Bcl-2 without p53 was observed in the group under irradiation only and the control group. Conclusion: β-Elemene is good at radiosensitization and its mechanism may be relevant to the up-regulation of P53, down-regulation of Bcl-2 and inducing apoptosis. Objective: To explore the effect and possible mechanism in vitro of radiosensitization by β-Elemene in A549 cell line from adenocarcinoma of lung. Methods: The A549 cell line from adenocarcinoma of lung was chosen for the study to determine the inhibition ratio by using MTT assay Change of cell cycle and apoptosis rate were analyzed by FCM and the expressions of gene P53 and Bcl-2 were detected. Results: Reproductive activity of the group which was under irradiation and β-Elemene was significantly sup- pressed and its cloning efficiency and divisional index also declined. The apoptosis rate of the group which was under irradia- tion and β-Elemene was significantly higher at 48 h and 72 h, which was analyzed by FCM . The expression of P53 without Bcl-2 was observed in the group under irradiation and β-Elemene and the group under β-Elemene only at the 48th hour point, while the expression of Bcl-2 Without p53 was observed in the group under irradiation only and the control group. Conclusion: β-Elemene is good at radiosensitization and its mechanism may be relevant to the up-regulation of P53, down-regulation of Bcl-2 and inducing apoptosis.