The erythroleukemic blast crisis in chronic myelogenous leukemia (CML) is rarely reported. We present two cases of erythroleukemic blast crisis of CML. In both cases, they had been treated with interferon and hydroxyurea prior to a blast crisis of CML. On blastic transformation, one patient underwent an acute clinical transformation marked with fever and hematochezia but the other showed no clinical deterioration. The blasts appeared in the peripheral blood. The bone marrow aspirates revealed megaloblastic erythroid hyperplasia (about 72%, 54% of all nucleated cells), increasing the number of myeloblasts (about 46%, 59% of all non-erythroid cells), and erythroblasts with a positive PAS stain. The cytogenetic studies revealed Philadelphia chromosomes with additional chromosomal abnormalities, t(3;21)(q26;q22) and the FISH studies revealed bcr-abl fusion signals in bone marrow cells. One case expired 8 months later despite of hydroxyuria therapy. The other case received allogeneic bone marrow transplantation (alloBMT) without complete remission but expired 34 weeks after alloBMT due to GVHD.