A case of acute eosinophilic leukemia (EoL) that occurred in a patient with preexistent myelodysplastic syndrome is reported. The patient was initially diagnosed as having refractory anemia (RA) on the basis of pancytopenia with dysplasia and chromosomal abnormalities. Two years later, he was readmitted because of progression of pancytopenia, and bone marrow and peripheral blood showed immature dysplastic eosinophils. Clonal assay of peripheral blood mononuclear cells revealed autonomous growth of colony-forming unit eosinophils. Cytotoxic chemotherapy did not induce remission, and extensive myelofibrosis developed. Cytogenetic analysis in the RA state showed +1p- and -7 whereas complicated abnormalities including +1p-, 3q- and 7p- dominated in the EoL state.