To investigate JAK2V617F mutation and its clinical significance in patients with idiopathic myelofibrosis (IMF), genomic DNA was extracted from peripheral blood cell samples of 12 IMF cases. Allele-specific PCR (AS-PCR) was performed to identify JAK2V617F mutation, and the results were confirmed by sequence analysis. A retrospective study was performed to explore the correlation between JAK2V617F mutation and the clinical, hematologic features. The results showed that in follow-up for 2 to 15 months, the occurrence of the positive point mutation in 12 patients with IMF was 50%, and the half of these positive patients had thrombosis. Patients with JAK2V617F point mutation had a higher counts of platelets and megakaryocytes in bone marrow than those in patients without JAK2V617F point mutation. Out of other 6 IMF patients without JAK2V617F point mutation only 1 patient had thrombosis, and lower counts of platelets in peripheral blood and megakaryocytes in bone marrow. It is concluded that majority of IMF patients with positive JAK2V617F point mutation have typical clinical and hematologic features, higher incidence of thrombosis, and higher counts of platelets in peripheral blood and megakaryocytes in bone marrow.