Objective: To study the impact of pegylated recombinant human granulocyte colony-stimulating factor (PEG-rhG-CSF) on hematology and marrow hemopoiesis in SD rat, and to provide an experimental basis for clinical trials. Methods: All rats were randomly divided into three experimental groups and one control group, then respectively administrated with different doses of PEG-rhG-CSF or vehicle control by sc injection once weekly for three months. After administration, two-week recovery period for all groups were followed. The examinations of hematological parameters and marrow were performed at the end of administration and recovery. The results were analyzed by t-test. Results: Compared with the vehicle control group, the leukocyte count (elevated 7.8--28.2 times), neutrophils count (elevated 2.5--3.9 times), and reticulocyte count were significantly increased in the high, middle, and low doses of groups at the end of administration,. In addition, the proportions of erythrocytes series, polychromatic erythroblast, and orthochromatic erythroblast in marrow were significantly decreased while the proportions of mature myeloid cell significantly increased (elevated 29.1%--79.1%). The ratios of myeloid series and erythrocytes series in marrow were also significantly elevated in all groups treated with PEG-rhG-CSF. These changes were restored to normal level after two-week recovery period. Conclusion: Our study suggest that PEG-rhG-CSF has a significant promotion on hemopoiesis function and can be applied for the clinical treatment of granulocytopenia induced by chemotherapy.