Abstract: Objective To explore whether thrombopoietin (TPO) can rescue megakaryopoiesis by protecting bone marrow�2;derived endothelial progenitor cells (BM-EPCs) in patients receiving chemotherapy for hematological malignancies. Methods Bone marrow samples were collected from 23 patients with hematological malignancies 30 days after chemotherapy and from 10 healthy volunteers. BM-EPCs isolated from the samples were identified by staining for CD34, CD309 and CD133, and their proliferation in response to treatment with TPO was assessed using CCK8 assay. DiL-Ac-LDL uptake and FITC-UEA-I binding assay were performed to evaluate the amount of BM-EPCs from the subjects. Tube-formation and migration experiments were used for functional assessment of the BM-EPCs. The BM-EPCs with or without TPO treatment were co-cultured with human megakaryocytes, and the proliferation of the megakaryocytes was detected with flow cytometry. Results Flow cytometry indicated that the TPO-treated cells had high expressions of CD34, CD133, and CD309. CCK8 assay demonstrated that TPO treatment enhanced the proliferation of the BM-EPCs, and the optimal concentration of TPO was 100 μg/L. Double immunofluorescence assay indicated that the number of BM-EPC was significantly higher in TPO-treated group than in the control group. The TPO-treated BM-EPCs exhibited stronger tube-formation and migration abilities (P<0.05) and more significantly enhanced the proliferation of co-cultured human megakaryocytes than the control cells (P<0.05). Conclusion TPO can directly stimulate megakaryopoiesis and reduce hemorrhage via protecting the function of BM-EPCs in patients following chemotherapy for hematological malignancies.