Objective: To figure out the effects of LY2405319, an analogue of fibroblast growth factor 21 (FGF21), on glucose homeostasis in streptozotocin (STZ)-induced insulin-depleted mice (STZ mice) Methods: Nine-weeks-old male C57BL/6J mice were administered a single intraperitoneal injection of STZ (150 mg/kg). One week later, heperglycemia induction was confirmed, and then saline or LY2405319 (5 mg/kg) was injected subcutaneously daily for 4 weeks. Alteration of glucose homeostasis, energy metabolism and brown adipose tissue (BAT) function were assessed. Results: The STZ mice showed elevated blood glucose and reduced plasma FGF21 levels, impaired glucose uptake in the BAT, and BAT mitochondria with absent or swollen cristae and fewer lipid vacuoles. LY2405319 significantly lowered blood glucose levels and it was associated with increased glucose uptake in BAT and changes in gene expression and morphology, indicating improved mitochondrial lipid metabolism in the BAT. Importantly, the ability of LY2405319 to lower blood glucose in STZ mice was compromised after removing interscapular BAT. Conclusion: Our results show that LY2405319 decreases blood glucose levels in insulin-deficient diabetes by improving BAT metabolism. Additional studies investigating the therapeutic potential of FGF21 for the treatment of type 1 diabetes are warranted.