Abnormal G-protein-coupled receptor kinase 2 (GRK2) accumulation has a crucial role in the development of insulin resistance and diabetes. Previous report showed that impaired insulin-induced relaxation in diabetes is improved by suppressing the GRK2 levels. Glucagon-like peptide-1 (GLP-1) is a gut hormone that promote insulin secretion. However, it is unknown whether GLP-1 directly affects diabetic endothelial dysfunction, especially GRK2 signaling. In this study, we investigated the relationship between GLP-1 and GRK2 under insulin stimulation for endothelial dysfunction. GLP-1 increased the impaired insulin-induced NO-dependent relaxation responses in diabetes. However, these responses are disappeared by treatment of Exendin-9, a GLP-1 receptor antagonist. Furthermore, phosphorylation levels of Akt and eNOS were higher in diabetes under GLP-1/insulin stimulation than non-stimulation. Additionally, in diabetes GRK2 activity was inhibited under GLP-1/insulin stimulation compared with non-stimulation, although GRK2 expression was not altered between the two groups. Those results suggest that in diabetes, GLP-1 improves the endothelial dysfunction by suppressing of GRK2 activity, which might provide a therapeutic target for diabetic vascular complications.