The mutant of human proinsulin gene(A4Glu→Leu) was recombinated to the expression vector and expressed in E.coli with high level.The expression product was purified by Sephadex G-50 gel filtration and converted to the mutant of human insulin by trypsin and carboxypeptidase B.The insulin mutant,purified by DEAE-Sephadex A-25,has an expected amino acid composition.The receptor binding activity and biological activity of this mutant are the same with that of standard porcine insulin.