Abstract: In order to solve the difficucties of renaturation and immunogenicity of new bifunctional fusion protein GAD, inclusion bodies of GAD were modified by PEG-maleimide. Conformational changes of the modified GAD were compared by circular dichroism and tryptophan fluorescence spectroscopy. The biological activity was verified by oral glucose tolerance test and lipid scavenging. The results showed that PEG-maleimide completed the specific-point modification of GAD, and improved its refolding efficiency. The secondary and tertiary structures of mPEGylated GAD were consistent with that of GAD. PEG-GAD has significant hypoglycemic and lipid-lowering effects(P<0. 001)with longer half life in vivo and lower immunogenicity(P<0. 01). This study provides effective strategies for the development of strongly hydrophobic peptide drugs.