Yi-Wei Wang,1,* Si-Jia He,1,* Xiao Feng,1 Jin Cheng,1 Yun-Tao Luo,1 Ling Tian,2 Qian Huang1 1The Comprehensive Cancer Center and Shanghai Key Laboratory for Pancreatic Diseases, Shanghai General Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, People’s Republic of China; 2Institute of Translational Medicine, Shanghai General Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, People’s Republic of China *These authors contributed equally to this work Abstract: Metformin is the most commonly prescribed drug for type 2 diabetes mellitus. In recent years, in addition to glucose lowering, several studies have presented evidence suggesting some potential role for metformin, such as antitumor effect, antiaging effect, cardiovascular protective effect, neuroprotective effect or an optional treatment for polycystic ovary syndrome. This paper will critically review the role of metformin to provide reference for doctors and researchers. Keywords: metformin, antitumor effect, antiaging effect, cardiovascular protective effect, neuroprotective effect, PCOS