Exendin-4 is an incretin mimetic that has been developed for the treatment of patients with type 2 diabetes. EXf is an available carboxy-terminal truncated fragment of exendin-4 with two amino acid substitutions. The purpose of these studies was to evaluate the biological activity of EXf. After a single subcutaneous injection, EXf significantly decreased plasma glucose concentration and glucose excursion following the administration of an oral glucose challenge both in non-diabetic (ICR), monosodium l-glutamate induced insulin resistance (MSG-IR) and diabetic KK-ay mice. Meanwhile, EXf resulted in an increase of first-phase insulin secretion in normal mice and KK-ay mice following the glucose challenge. EXf was also shown to inhibit small intestinal transit in rodent models. EXf activated the cAMP response element (CRE) of the rat insulin I gene promoter (RIP1) GFP-construct in a dose-dependent manner in the cultured mouse insulinoma cell line, termed NIT-1, and this agonist activity was blocked by the glucagon-like peptide 1 (GLP-1) receptor antagonist exendin(9-39). In summary, EXf, an analogue of exendin-4, has agonist activity to GLP-1 receptor in vitro and glucoregulatory activities in vivo, thus it can be considered as a new candidate for the treatment of type 2 diabetes.