Macaca mulatta granulocyte-macrophage colony stimulating factor (mGM-CSF) gene was synthesized, highly expressed in E. coli and the expressed product was purified.According to the E. coli-preferred codon, mGM-CSF gene was designed and synthesized, and cloned into prokaryotic expression vector pET-43.1a(+).The constructed recombinant plasmid pET-43.1a-mGM-CSF was transformed to E. coli BL21-CodonPlus (DE3)-RIPL and induced with IPTG.The expressed recombinant mGM-CSF was purified by Sephacryl S-200 mol. sieve chromatog., re-naturalized, then determined for reactogenicity by Western blot, and for biol. activity by MTT method.Both restriction anal. and sequencing proved that recombinant plasmid pET-43.1a-mGM-CSF was constructed correctly.The expressed recombinant protein, with a relative mol. mass of about 15 000, contained about 30% of total somatic protein and mainly existed in a form of inclusion body.The protein reached a purity of more than 95% after purification and re-naturalization, and showed specific binding to rat anti-human GM-CSF monoclonal antibody.The specific activity of the recombinant protein was 1.2×107 IU/mg.Recombinant mGM-CSF was successfully expressed in E. coli, which showed high biol. activity after purification and re-naturalization.