Abstract: Objective To evaluate the expression level of microRNA-125b (miR-125b) in gastric cancers and study its roles in cell proliferation and apoptosis. Methods The expression of miR-125b was detectable by real-time PCR in 40 gastric cancer tissues and paired cancer-adjacent tissues. The synthesized miR-125b mimic was transfected into cultured gastric cancer cell lines HGC-27 and MGC-803. The cell proliferation and apoptosis were measured by CCK-8 and flow cytometry respectively. Results MiR-125b was significantly up-regulated in gastric cancer tissues compared with cancer-adjacent controls（P<0.01）. Ectopic expression of miR-125b in HGC-27 and MGC-803 cells increased cell proliferation, whereas decreased cell apoptosis. Cells transfected for 72h, HGC-27（scramble：1.632±0.09，mimic：2.473±0.08），MGC-803（scramble：1.603±0.05，mimic：2.554±0.07）），Conclusion MiR-125b may act as an oncogene in gastric cancer via interfering with cell proliferation and apoptosis.

Key words: Keywords: microRNA-125b, gastric cancer, cell proliferation, cell apoptosis