The incidence of obesity is on the rise globally. Obesity has become a global disease that threatens human health and reduces the quality of human life. As a complicated disease affected by the interaction of genetic factors, environmental factors, and lifestyle, obesity can cause diseases such as hyperlipidemia, hypertension, cardiovascular diseases, metabolic syndrome, and non-alcoholic fatty liver disease. Metabolic activities of gut microbiota affect nutrition, metabolism, and immune functions of the host. Therefore, gut microbiota is an important environmental factor affecting obesity and metabolic disorders relevant to obesity. This paper reviews the relationships among gut microbiota, obesity, and metabolic disorders relevant to obesity and their affecting mechanisms.