Alpha-glucosidase inhibitors (α-GI) have abdominal signs which are generally regarded as side-reaction. The abdominal signs are caused by generation of intestinal gas which contains hydrogen gas. The hydrogen gas absorbed in the body eliminates oxidant stress and consequently the abdominal signs may have beneficial effects preventing onset and progression of arteriosclerosis. Recently, it has been reported that the combination therapy of dipeptidyl peptidase-4 inhibitors with a-GI enhances glucagon like peptide-1 (GLP- 1) secretion and increases active GLP-1 concentration. Therefore, α-GI is not only a matured and reliable oral anti-diabtic agent (OAD) but also a promising OAD which collaborates effectively with DPP-4 inhibitors or sodium-glucose cotransporter-2 inhibitors.