Acute Megakaryoblastic leukemia is a rare and rapidly fatal disease characterized by proliferation of megakaryocyte series and atypical megakaryocytes in the bone marrow. Acute Megakaryoblastic leukemia is suspicious when 1) megakaryocyte in peripheral blood, mixture of large and small mononuclear megakaryoblast in the bone marrow 2) cytoplasmic budding in blast 3) myelofibrosis (dense medullary overgrowth of reticulin fibers) 4) PAS(+), ANAE(+), SBB(-), peroxidase(-) and which is confirmed by platelet peroxidase oxidation on electromicroscope or monoclonal antibody. A case of aute megakaryoblastic leukemia was studied morphologically and monoclonal antibody.