Pure erythroid leukemia is a rare subtype of acute erythroid leukemia that is characterized by a predominant erythroid population, and erythroblastic sarcoma has not yet been described in the English literature. Here, we report a first case of erythroblastic sarcoma that presented as bilateral ovarian masses in a 3 ½-month-old infant girl with pure erythroid leukemia. Bone marrow aspirate and biopsy showed that the marrow was completely replaced by large-sized blasts consistent with erythroblasts. Immunophenotypically, both the tumor cells from the ovarian mass and bone marrow blasts were positive for CD117, glycophorin A, and hemoglobin A, demonstrating erythroid differentiation. Reverse transcriptase polymerase chain reaction showed that the tumor cells from ovarian mass expressed hemoglobin F and α1 spectrin, confirming their erythroid lineage. Conventional karyotype of the bone marrow aspirates revealed del(6)(q23q25) and trisomy 7 in all 21 cells examined. Fluorescence in situ hybridization of the ovarian mass demonstrated loss of c-myeloblastosis viral oncogene (C-MYB) at 6q23 locus in 41% of the cells, and deletion of chromosome 7 and 7q in 37% and 66% of cells, respectively. Taken together, we showed, for the first time, that pure erythroid leukemia presented as a myeloid sarcoma in the form of ovarian masses.