Abstract: Objective: To correctly understand the changes and of morphological characteristics of each stage of granulocytes after using granulocyte colony-stimulating factor (G-CSF), and avoid the wrong judgment. Method: Blood and bone marrow smears from venous blood and bone marrow of 30 patients with leucopenia after using G-CSF were stained by routine Raj staining, and morphological changes and characteristics of myeloid cells in the peripheral blood and bone marrow smear were observed by optical microscope. Result: After G-CSF stimulation, there were widespread nuclear left shift of granulocyte in the blood smear of patients. The number and morphology of various stages of granulocytes in bone marrow had more obvious changes:larger cell volume, higher cytoplasm content with basophilia, increased cytoplasmic granules with coarse grain and eosinophilia. Conclusion: After the application of G-CSF, there would be a series of number and morphology changes of granulocytes in the peripheral blood and bone marrow, which was a drug reaction, different from the morbidity hematopoiesis.