Orbital tumor formation in acute myeloid leukemia (AML) is rare as an initial symptom. Furthermore, orbital granulocytic sarcoma (myeloid sarcoma) in pediatric patients is uncommon. We describe a 5-year-old Japanese girl with a left orbital mass as an initial symptom of AML, the mass revealed by computed tomography. Peripheral blood and bone marrow pictures and a chromosomal analysis disclosing 46,XX,t(8;21)(q22;q22) showed AML (M2 according to the French-American-British classification). She was treated with antileukemic chemotherapy systemically. Three weeks after the initiation of chemotherapy, the orbital tumor regressed markedly. AML as an initial symptom of the orbital mass should be fully considered in a differential diagnosis, even in the absence of typical leukemic symptoms, and chromosomal analysis and immunophenotypical analysis may explain the pathogenesis of the extramedullary leukemic tumor.