The peripheral neutrophil recovery test was conducted to determine the efficacy of CJ-50001, a drug developed in Cheil Jedang R&D center as a recombinant granulocyte-colony stimulating factor (rG-CSF). Grasin was used as control drug. CJ-50001 and Gratin were subcutaneously administered to ${gamma}$-ray irradiated mice for 21 days at a dose of 10$mu$g/kg after bone marrow transplantation and the recovery of neutrophil number was examined on the days of 9, 13, 17, and 21 after the drug administration. It was observed that the peripheral neutrophil number of the vehicle control group was recovered to the normal level on the day of 13 after the transplantation whereas the group administered with CJ-50001 and Grasin respectively, showed the normal level of peripheral neutrophil number on 9th day after the bone marrow transplantation. The number of peripheral neutrophils reached the highest level on the 21 st day of drug administration, and was recovered to the normal level on the 4th day after ceasing of the drug administration (on the 25th day of the transplantation). Thus, it was presumed that CJ-50001 showed efficacy similar to Grasin on the peripheral neutrophil recovery after bone marrow transplantation.