Severe leukopenia was incidentally found in a newborn Japanese Black calf by blood testing during the clinical trial of an iron dextran drug (day 1). At that time, no clinical problems were observed. On day 15, the calf presented with a high rectal temperature and tachypnea. Treatment with antibiotics and non-steroidal anti-inflammatory drugs did not improve clinical signs. Anemia, melena, and prolonged bleeding were also recorded. Necropsy findings revealed subcutaneous petechial hemorrhage and severe bone marrow aplasia. This is the first confirmed case of pancytopenia and hemorrhage associated with bone marrow aplasia in a Japanese Black calf.