Abstract: Objective To report a case of aggressive natural killer （NK） cell leukemia with an aggressive clinical course. Methods Characteristics of aggressive NK cell leukemia and its treatment were discussed with a review of the literatures. Results The occurrence of aggressive NK cell leukemia was found to be higher in Asian. Most of its patients were young. The clinical features were found to be high fever and sweat involving the liver, spleen and lymph nodes and bone marrow, hypohepatia, reactive hemophagocytic syndrome, and hypocytosis, etc. Immunophenotype expressed CD2, CD7, CD16 and CD56. The prognosis of patients was very poor with a survival time of several weeks. Conclusion Aggressive NK cell leukemia is an unusual aggressive leukemia. Bone marrow puncture and biopsy should be performed, as well as immunophenotype and recombinant IGH gene, etc, should be detected to establish its diagnosis and start its treatment if aggressive NK cell leukemia is suspected.