Glucagon-like peptide 1 (GLP-1) and related peptide agonists have been extensively investigated for glycaemic control in Type 2 diabetes, and may also have therapeutic applications for other diseases. Due to the short half-life (t1/2 < 2 min) of the endogenous peptide, caused by proteolytic degradation and renal clearance, different strategies for half-life extension and sustained release have been explored. In the present study, conjugates between GLP-1 and a 5 kDa albumin-binding domain (ABD) derived from streptococcal protein G have been chemically synthesized and evaluated. ABD binds with high affinity to human serum albumin, which is highly abundant in plasma and functions as a drug carrier in the circulation. Three different GLP-1-ABD conjugates, with the two peptides connected by linkers of 2, 4 and 6 PEG units, respectively, were synthesized and tested in mouse pancreatic islets at high (11 mM) and low (3 mM) glucose concentration. Insulin release upon stimulation was shown to be glucose-dependent, showing no significant difference between the three different GLP-1-ABD conjugates and unconjugated GLP-1. The biological activity, in combination with the high affinity binding to albumin, make the GLP-1-ABD conjugates promising GLP-1 agonists expected to show extended in vivo half-life.