Dulaglutide (glucagon like peptide-1/IgG-Fc fusion protein, GLP-1-Fc) is a long lasting GLP-1 agonist, which consists of two arms of GLP-1 moieties fused to IgG Fc fragment. Dulaglutide is a safe and effective medication for type 2 diabetes. In an attempt to develop a biosimilar version of dulaglutide, we found that up to 75% of GLP-1-Fc displayed N -terminal truncations in one or both GLP-1 arms. We proposed that the N -terminal heterogeneity was caused by mis-cleavage of signal peptide and solved this problem through signal peptide optimization. Murine immunoglobulin kappa light chain signal peptide (KASP) significantly improves GLP-1-Fc N -terminal integrity and homogeneity. 92.8–95.7% of GLP-1-Fc molecules directed by KASP contain intact N -terminus. The productivity of GLP-1-Fc could reach 2.2 g/L in shaking flask fed batch culture. KASP is an optimal signal peptide for GLP-1-Fc expression in Chinese hamster ovary (CHO) cells.