Abstract： Objective To report clinical and laboratory features of a rare case who was primary myelofibrosis (PMF) with positive JAK2 V617F terminating in T-acute lymphoblastic leukemia (T-ALL).Methods A rare case of PMF terminating in ALL was found, the quantity and quality of JAK2 gene mutation were defined by PCR methods, collected the clinical dates. Results The JAK2 V617F gene mutations were all positive pre and post-blast, the mutant rates respectively were 71.21% and 83.56 %. The interval from PMF to leukemia was 22 months, and from leukemia to death was 27 days. Conclusion PMF with positive JAK2 V617F terminating in ALL is a rare case, clinical prognosis is poor and survival time is short.