Acquired hemophilia is a rare disorder caused by autoantibodies to factor VIII (FVIII) (also referred to as factor VIII inhibitors or anti-FVIII) and may be associated with pregnancy, underlying malignancy, or autoimmune disorders. A 33-month-old girl who presented with hematochezia and ecchymotic skin lesions was diagnosed with Mycoplasma pneumoniae pneumonia by serology and polymerase chain reaction. Hematologic studies showed a prolonged activated partial thromboplastin time (aPTT), partially corrected mixing test for aPTT, reduced levels of FVIII, and the presence of antibodies against FVIII. She was treated conservatively with prednisone and intravenous immunoglobulin (IVIG) without FVIII transfusion and recovered without sequelae. This report provides the first description of acquired hemophilia due to anti-FVIII in association with M. pneumoniae in Korea. We discuss this case in the context of the current literature on acquired hemophilia in children.