Recently, obesity is a well-recognized risk factor of type 2 diabetes and cardiovascular disease. There is more and more sufficient evidence that excess body weight is an avoidable cause of excess cancers including gastrointestinal, endometrial, esophageal adenocarcinoma, colorectal, postmenopausal breast, prostate, and renal cancers. The mechanism that obesity association with cancer is remains not well understood. There be some most studied hypothesized mechanisms such as, high levels of insulin and free levels of insulin-like growth factors (IGFs), sex hormones, adipocytokines, inflammatory cytokines, c-Myc (or Myc) oncogenic transcription factor, obesity-induced hypoxia and Warburg effect, and so on. In the future, the potential mechanisms and conclusions in obesity associated with increased risk for developing cancer, and the underlying cellular and molecular mechanisms will be studied. Recently, obesity is a well-recognized risk factor of type 2 diabetes and cardiovascular disease. There is more and more adequate evidence that excess body weight is an avoidable cause of excess cancers including gastrointestinal, endometrial, esophageal adenocarcinoma, colorectal, postmenopausal breast, prostate The mechanism that obesity association with cancer is remains not well understood. There are some most studied hypothesized mechanisms such as, high levels of insulin and free levels of insulin-like growth factors (IGFs), sex hormones, adipocytokines, inflammatory cytokines, c-Myc (or Myc) oncogenic transcription factor, obesity-induced hypoxia and Warburg effect, and so on. In the future, the potential mechanisms and conclusions in obesity associated with increased risk for developing cancer, and the underlying cellular and molecular mechanisms will be studied.