As JAK2 V617F, MPL W515L is a novel acquired mutation that induces constitutive cytokine-independent activation of the JAK-STAT pathway in myeloproliferative disorders (MPD). The discovery of this mutation provides a novel mechanism for activation of signal transduction in hematopoietic malignancies. To investigate its prevalence in Chinese patients with MPD, we introduced allele-specific PCR (AS-PCR) combined with sequence analysis to simultaneously screen MPL W515L and JAK2 V617F mutations in 190 MPD patients. MPL W515L mutation was found to be harbored in only one of 102 patients, who had essential thrombocythemia (ET, 1.0%) and was not detected in patients with polycythemia vera (PV), idiopathic myelofibrosis (IMF), and chronic myelogenous leukemia (CML). Sixty-eight BCR/ABL-negative MPD patients (46.3%) were found harboring JAK2 V617F mutation (PV, 62.5%; ET, 42.1%; IMF 38.1%). Furthermore, MPL W515L and JAK2 V617F mutations were not detected in patients of acute myeloid leukemia, acute lymphoblastic leukemia, myelodysplastic syndromes, and CML. It has been shown that MPL W515L mutations may contribute to the primary molecular pathogenesis of Chinese patients with ET.