Abstract: Objective :To investigate the clinicopathologic features, diagnosis and differential diagnosis of myeloid sarcoma. Methods :A study of clinicopathology and immunohistochemistry was done for 33 cases of myeloid sarcomas. Results :The cases were mainly solitary myeloid sarcomas or occuredconsistently with chronic myeloid leukemia; the involved sites included lymph nodes, skin, muscle,et al; Histologically, 30 cases were granulocytic sarcomas, 2 cases were monoblastic sarcomas and 1 case was biIifferentiation type.; Immunohistochemical analysis: all cases were positive for MPO and lysozyme, LCA,CD99,CD34 and CD68 were positive in some cases, Iii-67 PI (proliferative index)was 0.47±0.24. Conclusions :It is difficult to distinguish myeloid sarcoma from small round tumors morphologically, especially in absence of history of myeloid neoplasms. Immunohistochemistry is greatly essential for diag-nosis and differential diagnosis of myeloid sarcoma.