Granulocyte-macrophage colony-stimulating factor (GM-CSF) is a pleiotropic hematopoietic growth factor and an activator of mature myeloid cells, and recombinant GM-CSF is increasingly under clinical studies for the treatment of various diseases including cancer, infectious diseases and hematopoietic diseases. We constructed a recombinant mouse GM-CSF expression plasmid with pelB leader sequence and His.Tag under T7 promoter control, and showed that the construct produced a 20 kDa recombinant protein in 8M urea. We also showed that the 20 kDa recombinant protein prepared in 8M urea stimulated colony formation in vitro, indicating that the recombinant mGM-CSF can be renatured to its native form to show the colony stimulating activity.