Abstract: Metformin is the first-line oral drug for type 2 diabetes currently. While it plays an important role as an anti-diabetes drug，the anti-neoplastic activity of metformin has also been reported in epidemiological and animal studies in many cancers such as ovarian cancer，as it could reduce the risk of ovarian cancer and improve the survival rate. The mechanisms by which metformin exerts these effects are unknown, which may include decreasing fasting glucose and insulin level，activating the AMP-activated protein kinase （AMPK），inhibiting the mitochondrial complexⅠ，inducing cell cycle arrest，selectively killing the ovarian cancer stem cell and promoting apoptosis，etc. Many key problems need to be solved before the design of best clinical trials. Further laboratory investigation and large population prospective clinical trials are required to elucidate the mechanisms of metformin anti-neoplastic actions in ovarian cancer.

Key words: Metformin, Ovarian neoplasms, Diabetes mellitus, type 2, Mechanism, AMP-activated protein kinase