Abstract: Objective To investigate the effect of microRNA-7 overexpression on the apoptosis of human lung cancer cell line 95D in vitro and in vivo. Methods Eukaryotic expression vector encoding miR-7 (termed as p-miR-7) was transiently transfected into human lung cancer cell line 95D. TUNEL method was conducted to observe cell apoptosis. The phosphorylation of Caspase3 and Caspase9 protein were detected by immunofluorescence technology. Plasmid p-miR-7 was locally injected into tumor mass in nude mice model bearing human lung cancer cell line 95D. Then, cell apoptosis was detected by Hematoxylin and eosin staining and TUNEL method, respectively. Moreover, phosphorylation levels of Caspase3 and Caspase9 protein were determined by immunohistochemistry assay. Results miR-7 overexpression could lead to the apoptosis of lung cancer cells in vitro (P<0.05), accompanied by the increased phosphorylation levels of Caspase3 and Caspase9 proteins(P<0.05). After local injection of p-miR-7, both the expression level of miR-7 and the apoptosis of tumor cells were increased significantly(P<0.05). Moreover, phosphorylation levels of Caspase3 and Caspase9 protein were increased obviously(P<0.05). Conclusion miR-7 overexpression could lead to tumor cell apoptosis in vitro and in vivo, which is associated with increased phosphorylation levels of apoptosis related proteins Caspase3 and Caspase9.