We herein characterized the gut microbiomes in three of the most widely used mouse models of obesity/T2D, i.e., genetically induced (leptin-deficient i.e., Lepob/ob; and leptin-receptor-deficient i.e., Lepdb/db) and high-fat diet (HFD)-induced obese (DIO)/T2D mice, with reference to their normal chow-fed (NC) and low-fat-diet-fed (LF) control counterparts. The gene discussed is LEP; the disease is type 2 diabetes mellitus.