We investigated whether the peripheral co-administration of leptin and liraglutide (a glucagon-like peptide-1 receptor agonist) improved glucose metabolism in a mouse model of insulin-dependent diabetes mellitus (IDDM). Twelve-week-old male C57BL/6J mice were injected intraperitoneally with a high dose of streptozotocin to induce IDDM or vehicle-treated. Mice with IDDM were divided into four groups: leptin treatment alone (LEP), liraglutide treatment alone (LIRA), co-administration of leptin and liraglutide treatment (LEP+LIRA), untreated mice (UNT). Vehicle-treated mice were the healthy controls (HC). The blood glucose (BG) levels were measured, and a glucose tolerance test (GTT) was performed to compare the five groups. Leptin was administered peripherally at 20 μg/day using an osmotic pump, while liraglutide was administered subcutaneously at 1000 μg/kg/day. Monotherapy with leptin or liraglutide significantly improved glucose metabolism, as assessed by comparing BG levels and GTTs with those of the UNT group. Mice in the LEP+LIRA group showed even greater improvements in glucose metabolism than the monotherapy groups. Notably, glucose metabolism in the LEP+LIRA group improved comparably with the HC group. Thus, the peripheral co-administration of leptin and liraglutide effectively improved glucose metabolism in mice with IDDM without the use of insulin.