Abstract: A Reticulocyte Growth Factor (RGF) and a preparing method and application thereof is provided. The factor is separated and purified from impurities of ?1-antitrypsin (from human plasma), and the fragment of a precursor of the antitrypsin is determined, and has very high function of promoting the generation of the reticulocyte of mice. Monoclonal antibody of EPO is not combined with the reticulocyte growth factor, which is labeled with I125, after the reticulocyte growth factor is combined with surface receptors of mouse bone marrow cells, the EPO cannot compete with the reticulocyte growth factor. The EPO and RGF are labeled with different fluorochromes, and it is proved that they have different receptors.