Aim To prokaryotic express mouse obese gene in E.coli expression system and purify the fused mouse leptin.Methods Mouse obesity gene leptin was amplified from pMET mouse leptin and subcloned in pET-28a(+)to construct recombinant vector pET-28a-lep.The sequence of pET-28a-lep was checked by sequencing and restriction analysis.Expression of BL21-pET-lep transformed with pET-28a-lep was induced with 0.1 mmol/L isopropylthiogalactoside and analyzed with Sodium dodecylsulfonate-polyacrylamide gel electrophoresis and Western Blotting to identify the mouse leptin molecular weight and optimum time for purpose protein expression.The maximum amount of the fused protein expressed was examined with thin layer chromatography.Mouse leptin dissolved with 0.5% Sarkosyl was purified by Ni2+ affinity chromatography column.Results Sequencing and restriction analysis confirmed the right sequence of pET-28a-lep.Sodium dodecylsulfonate-polyacrylamide gel electrophoresis and Western Blotting indicated a 22.5 kDa fused mouse leptin,in the form of inclusion body,was expressed with high efficiency in BL21-pET-lep.The maximum amount of the fused protein produced was 39.2% of the total cellular protein.The concentration of purified protein is 1.086 g/L.Conclusion BL21-pET-lep could highly express recombinant mouse leptin.This provides a basis for further researches on biological activity of mouse leptin and its role on the developing process of arthrosclerosis.