Sleep disturbances are associated with type 2 diabetes; therefore, the amelioration of sleep may improve metabolic disorders. To investigate this possibility, we here examined the effects of suvorexant, an antiinsomnia drug targeting the orexin system, on sleep and glucose metabolism in type 2 diabetic mice. Diabetic db/db mice had a longer wakefulness time during the resting period, as compared with nondiabetic db/m+ control mice. The single or 7-day administration of suvorexant at lights-on (ie, the beginning of the resting phase) increased nonrapid eye movement sleep time during the resting phase and, as a consequence, reduced awake time. The daily resting-phase administration of suvorexant for 2-4 weeks improved impaired glucose tolerance in db/db mice without affecting body weight gain, food intake, systemic insulin sensitivity, or serum insulin, and glucagon levels. No changes were detected in the markers of lipid metabolism and inflammation, such as the hepatic triglyceride content and Tnf-α mRNA levels in liver and adipose tissues. The improving effect of suvorexant on glucose tolerance was associated with a reduction in the expression levels of hepatic gluconeogenic factors, including phosphoenolpyruvate carboxykinase and peroxisome proliferator-activated receptor-γ coactivator-1α in the liver in the resting phase. In contrast, the daily awake-phase administration of suvorexant had no beneficial effect on glucose metabolism. These results suggest that the suvorexant-induced increase of sleep time at the resting phase improved hepatic glucose metabolism in db/db mice. Our results provide insight into the development of novel pharmacological interventions for type 2 diabetes that target the orexin-operated sleep/wake regulatory system.