Objective To purify functional peptide Hepc25 of mouse and examine its expression by using the expression vector of prokaryote. Methods The gene of Hepc25 was fused with thioredoxin gene and the fusion protein was expressed greatly in E.ciol.Hepc25 gene amplification was done by RT-PCR and the gene was cloned into pET32a(+) plasmids. The pET-32a-Hepc25 plasmids were transformed into E.ciol BL21 competent cells.In order to obtain much of the fusion protein,the induction condition was optimized.The fusion protein was measured by SDS-PAGE and Western blotting.Isolation and purification of fusion protein were done by affinity chromatograph,iron exchange chromatography and exclusion chromatography.Purified Hepc25 from fusion protein hydrolyzed by enterokinase was analyzed by HPLC. Results BR>Fusion protein expression vectors were constructed successfully and the quantity of fusion protein was about 28% of total protein.Under the condition of 33℃,120 r/min,0.2 mmol/L isopropyl β-D-thiogalactopy ranoside(IPTG) for 8 hours,the quality of expression of fusion protein was the largest and the purity of fusion protein and Hepc25 were both over 95%. Conclusion Functional peptide Hepc25 of mouse is expressed by using prokaryotic expression vector and is purified.The optima exp