Abstract: ObjectiveTo investigate the effects of antidiabetic drug cimetidine on proliferation and apoptosis of human lung adenocarcinoma cell line A549 in vitro and explore the potential mechanisms. Methods A549 cell was treated with 0.5，1，5 and 10 mmol/L cimetidine for 48 h.Livability of the cells was measured by MTT assay.Cell apoptosis was detected by flow cytometry(FCM).Expressions of two proteins including Bcl-2 and Bax in the cells were measured by Western blot. Results The proliferation of A549 cell was inhibited by cimetidine in a dose-dependent manner and the apoptosis of cell was induced.The result of Western blot showed with the increasing cimetidine's concentration，the expression of Bcl-2 protein was decreased，the expression of Bax protein was increased. Conclusion Pretreatment with cimetidine can induce apoptosis of human lung adenocarcinoma A549 cell.The possible mechanism is through down-regulating the expression of Bcl-2 protein and up-regulating the expression of Bax protein.