This study aimed to determine the potential vascular protective effect of exendin-4, a synthetic glucagonlike peptide (GLP)-1 analogue, on the blood flow and remodelling of arteriovenous (AV) fistulas in a rat model of diabetes. AV fistulas were created in Sprague-Dawley rats with streptozotocin-induced diabetes. The animals were then randomly assigned to receive an intraperitoneal injection of vehicle (saline) or exendin-4 for about 2 weeks. The blood flow and vasomotor function of the aortic limb of the fistula were measured. Concentrations of serum norepinephrine and its associated tissue signal proteins, and vascular smooth muscle cell (VSMC) contractile proteins, matrix metalloproteinase (MMP)-2, and collagen expression in the remodelled aorta were examined. Exendin-4 attenuated the contraction response to phenylephrine in isolated arterial segments from treated animals. Treatment with exendin-4 increased serum norepinephrine concentration, reduced aorta tissue α1-receptor expression, and enhanced downstream signal proteins. Additionally, exendin-4 promoted the switching of VSMCs to the synthetic phenotype, which increased tissue collagen content and suppressed tissue abundances of smooth muscle myosin heavy chain type II and desmin in diabetic animals. In conclusion, our study demonstrated that exendin-4 modulates VSMC transition to the synthetic phenotype and enhances the arterial contraction responses, thereby attenuating blood flow in the AV fistula.