Monosomy 7 syndrome in infant is considered as pre-leukemic condition of poor prognosis. However, it seems controversial recently, because some cases of monosomy 7 syndrome showed spontaneous remission. We report 2-year-old girl with severe pancytopenia, who presented with monosomy 7. Morphologically, there was little dysplasia in the trilineage hematopoiesis. Monosomy 7 clone of CD34 positive cells, bone marrow mononuclear cells (BMMNC), and peripheral nuclear cells was 4.0, 40, and 3.8%, respectively. Immunosuppressive therapy was effective along with the disappearance of monosomy 7 clone. WT1 mRNA expression was not increased in monosomy 7 clone. Pathogenesis of monosomy 7 and its relation to aplastic anemia is discussed.