Six bases mutations were introduced into 5’ terminal of mature GM CSF gene by PCR in order to inhance the expression of GM CSF gene in E.coli . The expression product of the modified GM CSF gene in E.coli was accumulated mainly in the form of inclusion bodies and constitute dabout 13% of the total bacterial proteins. Western blotting demonstrated this product could combine specifically with monoclonal antibody against human GM CSF. After solubilization of purified inclusion bodies and renaturation of solubilized polypeptides

the authentic GM CSF with its purity above 99% was obtained by means of hydrophobic chromatography on Phenyl Sepharose CL 4B and gel filtrationon Sephadex G 100. The activity

measured by viable cell MTT staining method

was 1 28×10 7 u/mg. The purified product could maintain the growth of TF 1 cells which dependes on human GM CSF.