This study was aimed to investigate the JAK2V617F mutation in myeloproliferative disorders (MPD) and to evaluate the significance of JAK2V617F in diagnosis and therapy of MPD. The bcr/abl fusion gene in 70 MPD patients was detected by reverse transcription polymerase chain reaction (PT-PCR). The JAK2V617F mutation was detected by allele-specific polymerase chain reaction (AS-PCR) and the results were confirmed by sequence analysis. The results indicated that the bcr/abl fusion gene could be detected in 38 patients with chronic myeloid leukemia (CML), but not in the 32 none-CML patients. The JAK2V617F mutation was detected in 12 out of 16 (75%) patients with polycythemia vera (PV), 3 out of 10 (30%) patients with essential thrombocythemia (ET), 3 out of 6 (50%) patients with idiopathic myelofibrosis (IMF), but not in any of the CML patients. The JAK2V617F mutation frequencies between CML and bcr/abl negative MPD patients were statistically significant (p < 0.05). It is concluded that the JAK2V617F may be a characteristic molecular event in PV, ET and IMF patients which may serve as an important molecular marker for the diagnosis and classification of the three diseases.