We reported a newborn infant with macrophage activation syndrome (MAS) born from a mother with positive anti-nuclear (ANA) and anti-SSA/Ro antibodies. The 2,500 g girl was born at 37+6 weeks of gestation in good condition. Mother had been diagnosed with adult onset Still disease 10 years previously. During pregnancy, she did not take any medication as she was free of symptoms. The baby was admitted due to tachypnea and fever 12 h after birth. Initial laboratory findings showed mild anaemia with thrombocytopenia, and mild elevation of alanine aminotransferase (ALT). A work-up of infectious aetiology, including agents responsible for congenital infection, was negative. On the 10th hospital day (HD), the baby showed severe abdominal distension caused by hepatosplenomegaly, and persistent, high fever despite empirical antibiotic therapy. We identified positive ANA and anti-SSA/Ro antibodies from the infant, compatible with those found in the mother. The baby’s electrocardiography was normal. On the 18th HD, she showed deterioration of overall condition with high ferritin, ALT, and profound thrombocytopenia. The baby received intravenous immunoglobulin, steroid (pulse and oral), and cyclosporine. Gene study for perforin, K-ras, and N-ras was negative. Her general condition showed improvement after treatment, although mild fever and organomegaly remained. We maintained high dose steroid and cyclosporine, and all medication was tapered and stopped at 12 weeks of age. We suggest that transplacental transfer of maternal auto-antibodies may be associated with the infant’s MAS.