A 6-year-old girl with acute myelogenous leukemia (AML) developed fungal mandibular osteomyelitis during chemotherapy. Blastoschizomyces capitatus was recognized histologically by its yeast-like morphology and formation of annelloconidia, and was confirmed by culture. The fungal osteomyelitis of the mandible was treated successfully with prolonged antifungal medication, extensive surgical debridement and an oral care program, without interrupting leukemia chemotherapy. B. capitatus osteomyelitis of the mandible may occur during chemotherapy in AML patients with poor dental condition. Successful treatment can be achieved by careful management without interruption of antineoplastic chemotherapy.