Abstract: AIM: To accurately determine the purity and correctness of expression for the bulk samples and preparations of rHuGM-CSF with biological activity. METHODS: The purities of two bulk samples and three preparations of rHuGM-CSF were determined by capillary zone electrophoresis (CZE), molecular weights of two rHuGM-CSF bulk samples by matrix assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF/MS) and electrospray ionization mass spectrometry (ESI/MS), and isoelectric points of rHuGM-CSF bulk sample by capillary isoelectric focusing (CIEF). RESULTS: One of the two bulk samples was expressed incorrectly, and the other contained a small amount of dimer, which composed of four components with different isoelectric points. There were large amounts of impurities in the two rHuGM-CSF preparations. CONCLUSION: The sample of rHuGM-CSF with biologic activity may be expressed incorrectly or contained impurities. The instrumental methods applied in this paper are complementary and we can not use one to replace the other.