OBJECTIVE Even with great advances in modern medicine and therapeutic agent development, the search for effective antidiabetic drugs remains challenging. Coumarins are secondary metabolites found widely in nature plants and used mainly in anticoagulation and antithrombotic therapy. Over the past two decades, however, there has been an increasing body of literatures related to the effects of coumarins and their derivatives on diabetes and its complications. This review aimed to focus on research findings concerning the effects of coumarins against diabetes and its complications using in-vitro and in-vivo animal models, and also to discuss cellular and molecular mechanisms underlying these effects. RESULTS The search for new coumarins against diabetes and it complications, either isolated from traditional medicine or chemically synthesized, has been constantly expanding. The cellular and molecular mechanisms involved include protecting pancreatic beta cells from damage, improving abnormal insulin signalling, reducing oxidative stress/inflammation, activating AMP-activated protein kinase (AMPK), inhibiting α-glucosidases and ameliorating diabetic complications. CONCLUSIONS The effects and mechanisms of coumarins and their derivatives upon diabetes and its complications are discussed in current review. Further investigations remain to be carried out to develop a promising antidiabetic agent based on coumarin cores.