Insulin secretion and sensitivity play an essential role in maintaining normal glucose level and their abnormalities result in diabetes mellitus. H2S-synthesizing enzymes, CBS and/or CSE, are expressed in insulin-secreting pancreatic β cells and H2S inhibits insulin secretion by activating ATP-sensitive K+ channels. In addition, H2S has been reported to have either pro- or antiapoptotic effects on β cells. Studies in the animal models suggest that excess of H2S in pancreatic islets may contribute to both type 1 and type 2 diabetes. H2S has also been demonstrated to regulate insulin sensitivity. In the liver, H2S stimulates gluconeogenesis and glycogenolysis and inhibits glucose utilization and glycogen storage. Its effect on insulin-stimulated glucose uptake in the adipose tissue is controversial; both stimulation and inhibition have been reported. H2S may also regulate adipose tissue lipolysis, adipokine production and inflammation; the processes important for local and systemic insulin sensitivity. Little is known about the effect of H2S on skeletal muscle metabolism. High fat diet, obesity and insulin resistance affect CBS/CSE/H2S system in the liver and adipose tissue, although the effect depends on diet composition, animals species and time of high-fat feeding. Most studies indicate that blood H2S concentration decreases in animal models of diabetes and in diabetic humans.