The acute toxicity study of CJ-50001, a recombinant granulocyte-colony stimulating factor (rG-CSF), was performed in Sprague Dawley (SD) rats and beagle dogs. CJ-50001 was administered up to maximum dose 5,000 $mu extrm{g}$/kg (i.v.) and 10,000 $mu extrm{g}$/kg (p.o.) in SD rats and 5,000 $mu extrm{g}$/kg (i.v.) in beagle dogs. In these experiments, there were no death and harmful clinical changes which were related to CJ-50001. In conclusion, $LD_{50}$ of CJ-50001 is over 5,000 $mu extrm{g}$/kg, i.v. in SD rats and beagle dogs, and over 10,000 $mu extrm{g}$/kg, p.o. in SD rats.