Abstract: The present invention relates to a fusion protein in which transferrin is peptide-bonded to a terminal of a granulocyte-colony stimulating factor (G-CSF) protein or a G-CSF mutant protein in which the 116th threonine is substituted with cysteine in the amino acid sequence of the G-CSF. Specifically, the granulocyte-colony stimulating factor (G-CSF) mutant protein of the present invention or the transferrin fusion protein thereof displays a significantly increased specific activity and blood stability, compared with the conventional human G-CSF, and has a higher purification efficiency than the conventional PEGylated G-CSF characterized by the extended half-life, so that it can be advantageously used for preventing or treating ischemic diseases or neutropenia.