Macrophage Activating Syndrome (MAS) is a life-threatening disease seen in autoimmune diseases including lupus erythematosus, rheumatoid arthritis, Still's disease, polyarteritis nodosa. It is characterized by fever, pancytopenia, liver failure, coagulopathy, and neurologic symptoms and high serum ferritin. A 27 yr. old female patient was admitted in shahid Mostafa Khomeini Hospital (Tehran-Iran) in May 2011 because of lower extremities edema and ascites and fever from 1.5 month ago. In physical examinations she had generalized lymphadenopathy, splenomegaly and pleural effusion. In laboratory tests she had pancytopenia, positive ANA and Anti DNA (ds), hypocomplementemia, hypertriglyceridemia and high ferritin level. Gradually she had signs of RPGN and ARDS. The patient had no skin and musculoskeletal signs of SLE and no liver failure nor coagulopathy of MAS. Her lymph node biopsy was reported as Castleman syndrome. Unlike other studies, the patient showed MAS before treatment with cytotoxic for lupus nephritis.