Abstract： Objective To investigate the expression and clinical significance of P-selectin (CD62P) in bone marrow hematopoietic stem cells of patients with acute leukemia (AL). Methods The CD62P expression in bone marrow mononuclear cells of 15 healthy donors and 56 untreated patients with AL, were examined by flow cytometry. Results The average rate of CD62P expression was (6.72±7.64) % in hematopoietic stem cells (CD+45 CD+34 CD-38) of the 38 patients with acute myeloid leukemia (AML), was (3.46±2.51) % in hematopoietic stem cells (CD+45 CD+34 CD+19) of the 12 patients with B-acute lymphoblastic leukemia (B-ALL), and was (6.23±4.95) % in hematopoietic stem cells (CD+45 CD+34 CD+7) of 6 patients with T-acute lymphoblastic leukemia (T-ALL). The expression rates in those AL patients were higher than that in the healthy controls (1.04 ±1.23) % (t = 2.847, 3.284, 3.091, respectively, P ＜0.01), while there was no difference between the control group and the group who reach CR after routine treatment (t =1.932, P ＞0.05). Furthermore, the leukocyte,hemoglobin and platelet count in CD+62P patients with AML and T-ALL were significantly higher than CD-62P ones (t =4.153, 8.095, 8.289, 7.235, 8.692, 9.832, respectively, P ＜0.05), but there was no significant difference between CD+62P and CD-62P patients with B-ALL (t =0.340, 1.142, 0.019, respectively, P ＞0.05).Conclusion The CD62P is one of the markers of platelet activation, and its expression varies in different types of AL. The CD62P in hematopoietic stem cells of AL could be regarded as a new sign for the leukemic stem cells, as well as a helpful prognostic indicator in treatment response assessment.