Objective: To investigate the relationships and clinical significance among level of serum Thrombopoietin (TPO) 、peripheral blood platelet counts and megakaryocyte counts in patients with thrombocytopenia. Methods: Level of TPO、platelet counts and megakaryocyte counts in 50 patients with thrombocytopenia and 20 healthy volunteers (normal controls) were detected by a sandwich- ELISA procedure、automatic hemocytoanalyser and handmade count.Results: The serum TPO levels in idiopathic thrombocytopenic purpura (ITP) were low lightly compared to those in normal controls (P0.05); The serum TPO levels in second thrombocytopenia (ST) were higher than those in normal controls (P0.05); The blood platelet counts and megakaryocyte counts in ITP and ST were negative correlate with TPO level(P0.05).Conclusion: Serum TPO levels measurements have certain diagnostic value in thrombocytopenia.Serum TPO levels were regulated by platelet counts and megakaryocyte counts.