Abstract: Breast cancer is the second leading cause of death in women and is the most common cancer among women. Large amounts of clinical studies and epidemiological data have confirmed that obesity is closely related to the development and progression of breast cancer，and its pathogenesis is associated with many kinds of obesity related factors，such as estrogen，insulin，insulin-like growth factor-1（IGF-1），adiponectin，leptin，inflammatory factor and etc. Recently，research on obesity and mechanism to promote the development of breast cancer has carried on thoroughly; and the important influence of obesity on breast cancer diagnosis，tumor characteristics，prognosis and treatment is further understood. Weight control，therefore，may be a positive measure to prevent recurrence and metastasis; maintain a normal body weight can contribute to the prophylaxis of breast cancer.