Factor XIII (FXIII) is the final enzyme in the coagulation cascade. Acquired FXIII deficiency is caused by inhibitors of FXIII or decreased synthesis and/or increased consumption of FXIII, which leads to severe bleeding. Recently, we experienced a case of hemorrhagic-acquired factor XIII deficiency that occurred during treatment with the IL-6 inhibitor tocilizumab for rheumatoid arthritis. A 48-year-old man was referred because of right hip pain due to a hematoma. Laboratory findings showed that routine coagulation tests were normal, while FXIII activity was slightly low (52.4 %). The patient was successfully treated with plasma-derived factor XIII concentrates. The time course of recovery suggests that tocilizumab might have inhibited FXIII production. To our knowledge, this is the first report of acquired factor XIII deficiency associated with administering of tocilizumab. When recurrent bleeding is seen during administering of tocilizumab, acquired factor XIII deficiency may have been induced, thus attending physicians should consider this disease in a differential diagnosis.