Exendin-4, a peptide analogue of glucagon-like peptide (GLP-1), has been developed for treatment of type 2 diabetes. Herein, the secretive exendin-4 peptide, expressed by methanol induction in Pichia pastoris, was purified to near homogeneity by Ni-NTA agarose chromatography. 103.6 mg of protein was obtained from 1 L of the supernatant and its purity was 96.1%. Subsequently, the PEGylated exendin-4 was prepared. The bioactivity of exendin-4 was determined by examining the glucose-lowering and insulin-releasing ability in plasma. Then, a safety evaluation was performed by histological examination of the main organs (liver, kidney and pancreas). PEGylated exendin-4 displayed glucose-lowering and insulin-stimulating action in vivo without obvious damage to the above organs. The results suggest that the P. pastoris expression could be used to produce large quantities of exendin-4 and PEGylation is a useful tool to maintain and enhance bioactivity of the peptide.