A 17-year-old woman was previously diagnosed with autoimmune hepatitis (AIH) by liver biopsy. Adult-onset Still's disease (AOSD) was subsequently diagnosed on the basis of high fever, arthralgia, erythema, leukocytosis (>80% granulocytes), cervical lymph node swelling, splenomegaly, and hyperferritinemia. Her symptoms and liver dysfunction improved with prednisolone of 60 mg daily and subsequently methotrexate was added. However her symptoms and liver dysfunction relapsed when prednisolone was tapered to 20 mg/day. Therefore infliximab was introduced additionally and her symptoms and liver dysfunction subsided. To our knowledge, this is the first reported case of AOSD with AIH diagnosed by liver biopsy.